Low-loss magnetic powder core, and switching power supply, active filter, filter, and amplifying device using the same

ABSTRACT

A magnetic powder core comprises a molded article of a mixture of a glassy alloy powder and an insulating material. The glassy alloy comprises Fe and at least one element selected from Al, P, C, Si, and B, and has a texture primarily composed of an amorphous phase. The glassy alloy exhibits a temperature difference ΔT x , which is represented by the equation ΔT x =T x −T g , of at least 20 K in a supercooled liquid, wherein T x  indicates the crystallization temperature and T g  indicates the glass transition temperature. The magnetic core precursor is produced mixing the glassy alloy powder with the insulating material, compacting the mixture to form a magnetic core precursor, and annealing the magnetic core precursor at a temperature in the range between (T g −170) K and T g  K to relieve the internal stress of the magnetic core precursor. The glassy alloy exhibits low coercive force and low core loss.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to magnetic powder cores and tomethods for making the same. In particular, the present inventionrelates to a low-coercive-force, low-loss magnetic powder core and amethod for making the same. The present invention also relates toswitching power supplies, various converter circuits, and activefilters. Furthermore, the present invention relates to filters andamplifying devices, and particularly, relates to a low-loss filteroutputting less distorted waveforms.

[0003] 2. Description of the Related Art

[0004] As magnetic cores used in core components, such as transformercores for switching power supplies and smoothing choke cores, whichrequire a constant permeability up to the high frequency region, ferriteclosed-magnetic-circuit cores, ferrite gapped cores, andamorphous-alloy-tape-wound cores provided with gaps have been proposed.Also, magnetic powder cores formed by compacting a mixture of a powder,such as carbonyl iron, permalloy, or sendust, and an insulating materialhave been proposed.

[0005] Ferrite sintered magnetic cores exhibit low core loss, butsimultaneously exhibit small saturation magnetic flux densities. Thus,in ferrite closed-magnetic-circuit cores and ferrite gapped cores, aleakage magnetic flux from the gap section adversely affects peripheralelectric circuits. Magnetic powder cores using powders of carbonyl iron,permalloy, and sendust have the disadvantage of large core loss,although the cores exhibit higher saturation magnetic flux densitiescompared to ferrite magnetic cores.

[0006] In recent years, development of electronic devices has advancedwith an increase in the use thereof. In particular, the weight of thedevelopment was shifted toward reducing heat dissipation by reducing thesize of the electronic devices and reducing the power loss. In order toachieve these aims, switching power supplies, various DC/DC convertercircuits, and active filters have been improved. These devices usevarious types of magnetic elements having magnetic cores. Ferrite ismainly used for the magnetic cores. In some cases, carbonyl ironmagnetic cores, FeAlSi-alloy magnetic powder cores, and FeNi-alloymagnetic powder cores are also used.

[0007] A ferrite magnetic core is generally provided with a gap toprevent magnetic saturation. A leakage magnetic flux from the gap willadversely affect peripheral circuits. On the other hand, a NiZn ferritecore exhibits a large core loss, resulting in high heat dissipation froma device using this core. A carbonyl magnetic powder core exhibits anextremely large core loss, resulting in significantly high heatdissipation compared to ferrite magnetic cores. In addition, in aFeAlSi-alloy magnetic powder core and a FeNi-alloy magnetic powder core,the core loss thereof is lower than that of the carbonyl iron magneticpowder core, but still does not reach required levels.

[0008] Low-pass filters have been used for smoothing the pulse shapeoutput from impulse modulation amplifiers. The requirements for low-passfilters are low loss and less distortion of smoothed waveforms. Alow-pass filter is generally provided with a capacitor and an inductorcomposed of a coil with a magnetic core. Achievement of theserequirements strongly depends on properties of the magnetic coreconstituting the inductor. Thus, conventional low-pass filters useamorphous magnetic cores provided with gaps, ferrite cores provided withgaps, or carbonyl iron gap-free magnetic powder cores.

[0009] However, in filters using amorphous magnetic cores provided withgaps or ferrite cores provided with gaps, leakage magnetic fields fromthe gaps may adversely affect peripheral elements and circuits,resulting in decreased stability in the entire circuits including thefilters and generation of noise. Moreover, in these filters, theamplitude permeability varies with changes in the magnetic field andexhibits a large rate of change. When a pulsed current causing a largechange in magnetic field is smoothed, the waveform will be significantlydistorted.

[0010] In the carbonyl iron gap-free magnetic powder cores, thedependence of the amplitude permeability on the magnetic field isconstant, and the waveform is not distorted. However, the carbonyl irongap-free magnetic powder cores dissipate a significant amount of heatdue to large core loss.

[0011] The large core loss in conventional magnetic powder cores is dueto large core loss of the magnetic materials themselves used for themagnetic powder and insufficient relaxation of stress which is appliedduring compacting of the magnetic powder cores.

SUMMARY OF THE INVENTION

[0012] Accordingly, it is an object of the present invention to providea magnetic powder core having low coercive force and low core loss and amethod for making the same.

[0013] It is another object of the present invention to provide aswitching power supply, converter circuits, and active filters whichexhibit low heat dissipation and which can be miniaturized.

[0014] It is another object of the present invention to provide a filterwhich dissipates less heat due to low loss and which suppresses waveformdistortion, and an amplifying device provided with this filter.

[0015] According to a first aspect of the present invention, a magneticpowder core comprises a molded article of a mixture of a glassy alloypowder and an insulating material, the glassy alloy comprising Fe and atleast one element selected from Al, P, C, Si, and B, having a textureprimarily composed of an amorphous phase, and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0016] Since the magnetic powder core of the present invention comprisesa mixture of the glassy alloy powder and the insulating material, theinsulating material enhances the resistivity of the entire magneticpowder core. Thus, the magnetic powder core exhibits reduced core lossdue to reduced eddy current loss and high permeability in ahigh-frequency region.

[0017] Preferably, the glassy alloy has a resistivity of at least 1.5μΩ•m. The eddy current loss in the glassy alloy particles in ahigh-frequency region is thereby effectively decreased, the magneticpowder core exhibiting further reduced core loss.

[0018] The magnetic powder has a coercive force of preferably 80 A/m orless and more preferably 40 A/m or less in an applied magnetic field of±2.4 kA/m.

[0019] Preferably, the magnetic powder core has a core loss of 400 kW/m³or less under the conditions of a frequency of 100 kHz and a magneticflux density of 0.1 T. This core loss is significantly smaller than thatof known magnetic powder cores.

[0020] Preferably, the insulating material comprises a silicone rubber.The silicone rubber is effective for relieving the internal stress ofthe magnetic powder core.

[0021] Preferably, the glassy alloy is represented by the followingformula:

(Fe_(1-a)T_(a))_(100-x-v-z-w)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w)

[0022] wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

[0023] The magnetic powder core of the present invention is formed ofthe above Fe-based glassy alloy powder in which the Fe content is higherthan the Co and/or Ni content. Since this Fe-based glassy alloy exhibitshigher saturation magnetic flux density than that of a Co-based glassyalloy, the magnetic powder core exhibits further improved magneticcharacteristics.

[0024] According to a second aspect of the present invention, a methodfor making a magnetic powder core comprises a powder preparation step ofpreparing a powder of a glassy alloy comprising Fe and at least oneelement selected from Al, P, C, Si, and B, having a texture primarilycomposed of an amorphous phase, and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature, a molding step of mixing the glassy alloy powder with aninsulating material and compacting the mixture to form a magnetic coreprecursor, and an annealing step of annealing the magnetic coreprecursor at a temperature in the range between (T_(g)−170) K and T_(g)K to relieve the internal stress of the magnetic core precursor.

[0025] Preferably, the magnetic core precursor is annealed at atemperature between (T_(g)−140) K and (T_(g)−60) K in the annealingstep. The internal stress formed in the glassy alloy or the magneticcore precursor during the powder preparation step or the molding step isrelieved without crystallization of the glassy alloy.

[0026] More preferably, the magnetic core precursor is annealed at atemperature between (T_(g)−140) K and (T_(g)−60) K. When the magneticcore precursor is annealed at a temperature in the above range, theresulting magnetic powder core exhibits a coercive force of 80 A/m orless in an applied magnetic field of ±2.4 kA/m.

[0027] More preferably, the magnetic core precursor is annealed at atemperature between (T_(g)−110) K and (T_(g)−60) K. When the magneticcore precursor is annealed at a temperature in the above range, theresulting magnetic powder core exhibits a coercive force of 40 A/m orless in an applied magnetic field of ±2.4 kA/m.

[0028] In this method, the glassy alloy is preferably represented by thefollowing formula:

(Fe_(1-a)T_(a))_(100-x-v-z-x)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w)

[0029] wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

[0030] According to a third aspect of the present invention, a switchingpower supply comprises a switching element for converting a DC voltageinto a rectangular waveform voltage, a transformer for transforming therectangular waveform voltage, and a rectification circuit and asmoothing circuit for converting the transformed rectangular waveformvoltage into a DC voltage, wherein the transformer comprises a magneticcore comprising a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy powder having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0031] Since the switching power supply of the present inventionincludes a transformer having a magnetic core composed of a glassy alloypowder and an insulating material, the internal stress of the magneticcore can be relieved by annealing at a temperature which is sufficientlylower than the crystallization temperature of the glassy alloy, and theheat dissipation from the entire switching power supply can be reduceddue to reduced core loss.

[0032] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation, and does not generate a leakagemagnetic field which adversely affects other peripheral circuit.

[0033] According to a fourth aspect of the present invention, aswitching power supply comprises a switching element for converting a DCvoltage into a rectangular waveform voltage, a transformer fortransforming the rectangular waveform voltage, and a rectificationcircuit and a smoothing circuit for converting the transformedrectangular waveform voltage into a DC voltage, wherein the smoothingcircuit comprises a capacitor and a coil provided with a magnetic core,the magnetic core comprising a molded article of a mixture of a glassyalloy powder and an insulating material, the glassy alloy powdercomprising Fe and at least one element selected from Al, P, C, Si, andB, having a texture primarily composed of an amorphous phase, andexhibiting a temperature difference ΔT_(x), which is represented-by theequation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid,wherein T_(x) indicates the crystallization temperature and T_(g)indicates the glass transition temperature.

[0034] Since the switching power supply of the present inventionincludes a transformer having a magnetic core composed of a glassy alloypowder, the internal stress of the magnetic core can be relieved byannealing at a temperature which is sufficiently lower than thecrystallization temperature of the glassy alloy, and the heatdissipation from the entire switching power supply can be reduced due toreduced core loss.

[0035] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation, and does not generate a leakagemagnetic field which adversely affects other peripheral circuit.

[0036] According to a fifth aspect of the present invention, a step-downconverter circuit comprises a switching element, a coil provided with amagnetic core generating a back electromotive force when the switchingelement breaks a DC current, a capacitor for smoothing a currentgenerated by the back electromotive force, and a rectifying elementconnected to the coil provided with the magnetic core in an antiparallelstate, the rectifying element, the coil provided with the magnetic core,and the capacitor constituting a circulating current path, wherein themagnetic core comprises a molded article of a mixture of a glassy alloypowder and an insulating material, the glassy alloy having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0037] According to a sixth aspect of the present invention, a boostingconverter circuit comprises a switching element, a coil provided with amagnetic core generating a back electromotive force when the switchingelement breaks a DC current, a rectifying element connected in series inthe forward direction to the coil provided with the magnetic core forrectifying a current generated by the back electromotive force, and acapacitor for smoothing the rectified current, wherein the magnetic corecomprises a molded article of a mixture of a glassy alloy powder and aninsulating material, the glassy alloy having a texture primarilycomposed of an amorphous phase and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.

[0038] According to a seventh aspect of the present invention, apolarity-reversing converter circuit comprises a switching element, acoil provided with a magnetic core generating a back electromotive forcewhen the switching element breaks a DC current, a capacitor forsmoothing a current generated by the back electromotive force, and arectifying element connected in series in the backward direction to thecoil provided with the magnetic core for blocking the DC current,wherein the magnetic core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy havinga texture primarily composed of an amorphous phase and exhibiting atemperature difference ΔT_(x) which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0039] In the step-down converter circuit, the boosting convertercircuit, and the polarity-reversing converter circuit, a magnetic corecomposed of a glassy alloy powder is used. Thus, the internal stress ofthe magnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire switching power supplycan be reduced due to reduced core loss.

[0040] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation, and does not generate a leakagemagnetic field which adversely affects other peripheral circuit.

[0041] According to an eighth aspect of the present invention, an activefilter comprises the above-described boosting converter circuit, and acontrol unit for controlling the switching interval of the switchingelement of the boosting converter circuit.

[0042] The active filter of the present invention uses a coil with amagnetic core composed of a glassy alloy powder in the converter circuittherein. Since this magnetic core exhibits low loss, the heatdissipation from the entire active filter can be reduced.

[0043] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation, and does not generate a leakagemagnetic field which adversely affects other peripheral circuits.

[0044] In the above aspects, the magnetic core exhibits low core lossand low permeability, reducing heat dissipation. Moreover, the magneticcore exhibiting low permeability does not require a gap for preventingmagnetic saturation, and does not generate a leakage magnetic field,which adversely affects other peripheral circuit.

[0045] Moreover, the insulating material enhances the resistivity of theentire magnetic core and further reduces core loss due to reduced eddycurrent loss.

[0046] According to a ninth aspect of the present invention, a filtercomprises a capacitor and an inductor of a coil wound around a magneticcore, wherein the magnetic core comprises a molded article of a mixtureof a glassy alloy powder and an insulating material, the glassy alloyhaving a texture primarily composed of an amorphous phase and exhibitinga temperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0047] In this filter, the internal stress of the glassy alloy can berelieved by annealing at a temperature which is sufficiently lower thanthe crystallization temperature of the glassy alloy, and the magneticcore exhibits low core loss and a substantially constant amplitudepermeability over a wide intensity range of magnetic field. Thus, thefilter exhibits reduced heat dissipation and outputs less distortedwaveforms.

[0048] Moreover, the insulating material enhances the resistivity of theentire magnetic core and further reduces core loss due to reduced eddycurrent loss. Since high permeability is maintained in a high-frequencyregion, the filter exhibits further improved high-frequencycharacteristics.

[0049] Preferably, the rate of change in amplitude permeability of themagnetic core in a magnetic field of 2,000 A/m is within ±10% of anamplitude permeability in a magnetic field of 200 A/m, and thepermeability of the magnetic core at 100 kHz is in the range of 50 to200.

[0050] The filter outputs less distorted waveforms. Thus, the filter ispreferably applicable to a smoothing circuit of a pulse width modulatingamplifier.

[0051] Preferably, the filter is a low-pass filter. That is, thecapacitor and the inductor are connected into an L shape.

[0052] Preferably, the glassy alloy is represented by the followingformula:

(Fe_(1-a2)T_(a2))_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)

[0053] wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0≦b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

[0054] Since the magnetic core composed of the glassy alloy having theabove composition exhibits reduced core loss and a substantiallyconstant amplitude permeability over a variable magnetic field, thefilter using the magnetic core exhibits reduced loss and reduced heatdissipation, and outputs waveforms with less distortion.

[0055] According to a tenth aspect of the present invention, anamplifying device comprises an amplifier for outputting a pulsed currentand a filter connected to the output side of the amplifier for smoothingthe pulsed current, wherein the filter comprises a capacitor and aninductor of a coil wound around a magnetic core, wherein the magneticcore comprises a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy having a texture primarilycomposed of an amorphous phase and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.

[0056] In the amplifying device of the present invention, the magneticcore composed of the glassy alloy powder and the insulating material.The internal stress of the magnetic core can be relieved by annealing ata temperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theamplifying device can be reduced due to reduced core loss. Theamplifying device outputs waveforms with less distortion.

[0057] Moreover, the insulating material enhances the resistivity of theentire magnetic core and further reduces core loss due to reduced eddycurrent loss. Since high permeability is maintained in a high-frequencyregion, the filter exhibits reduced loss and outputs waveforms with lessdistortion.

[0058] Preferably, the rate of change in amplitude permeability of themagnetic core in a magnetic field of 2,000 A/m is within ±10% of anamplitude permeability in a magnetic field of 200 A/m, and thepermeability of the magnetic core at 100 kHz is in the range of 50 to200.

[0059] Within the above rate of change, the output waveform from theamplifying device is less distorted. Moreover, the number of turns ofthe coil can be reduced, thus resulting in a reduction in size of theamplifying device.

[0060] Preferably, the filter is a low-pass filter.

[0061] Preferably, the amplifier is a pulse-width-modulation amplifier.

[0062] preferably, the glassy alloy is represented by the followingformula:

(Fe_(1-a2)T_(a2))_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)

[0063] wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0≦b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

[0064] Since the magnetic core composed of the glassy alloy having theabove composition exhibits reduced core loss and a substantiallyconstant amplitude permeability over a variable magnetic field, theamplifying device using the magnetic core exhibits reduced loss andoutputs waveforms with less distortion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0065]FIG. 1 is an isometric view of an embodiment of a magnetic powdercore in accordance with the present invention;

[0066]FIG. 2 is an isometric partially broken-away view of a mold usedin the production of a magnetic powder core in accordance with thepresent invention;

[0067]FIG. 3 is a schematic cross-sectional view of a discharge plasmasintering apparatus used in the production of a magnetic powder core inaccordance with the present invention;

[0068]FIG. 4 is a graph illustrating X-ray diffraction patterns of atape and a powder of a glassy alloy having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃;

[0069]FIG. 5 is a DSC thermogram of a tape and a powder of a glassyalloy having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃;

[0070]FIG. 6 is a graph illustrating the dependence of the magnetic fluxdensity on the annealing temperature of a magnetic powder corecontaining a glassy alloy having a composition ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and an insulating layer in accordancewith the present invention;

[0071]FIG. 7 is a graph illustrating the dependence of the coerciveforce on the annealing temperature of a magnetic powder core containinga glassy alloy having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃and an insulating layer in accordance with the present invention;

[0072]FIG. 8 is a graph illustrating the dependence of the magnetic fluxdensity on the annealing temperature of a magnetic powder core forcomparison containing powdered iron and an insulating layer;

[0073]FIG. 9 is a graph illustrating the dependence of the coerciveforce on the annealing temperature of a magnetic powder core forcomparison containing powdered iron and an insulating layer;

[0074]FIG. 10 is a graph illustrating the dependence of the permeability(μ′) on the frequency (f) of a magnetic powder core containing a glassyalloy having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and aninsulating layer in accordance with the present invention;

[0075]FIG. 11 is a graph illustrating the dependence of the core loss(W) on the frequency (f) of a magnetic powder core containing a glassyalloy having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ and aninsulating layer in accordance with the present invention;

[0076]FIG. 12 is a graph illustrating the dependence of the permeability(μ′) on the frequency (f) of a magnetic powder core containing powderediron and an insulating layer;

[0077]FIG. 13 is a graph illustrating the dependence of the core loss(W) on the frequency (f) of a magnetic powder core containing powderediron and an insulating layer;

[0078]FIG. 14 is a ternary diagram illustrating the dependence of theglass transition temperature T_(g) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) of a glassy alloy tape;

[0079]FIG. 15 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) of a glassy alloy tape;

[0080]FIG. 16 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the compositionFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w) in a supercooled liquid of aglassy alloy tape;

[0081]FIGS. 17A and 17B are graphs illustrating the dependence of thepermeability μ′ and the rate of change therein Δμ′, respectively, on theDC magnetic field H of a magnetic powder core;

[0082]FIGS. 18A and 18B are graphs illustrating the dependence of theinductance L and the rate of change therein ΔL, respectively, on the DCbias magnetic field H_(dc) of a magnetic powder core;

[0083]FIGS. 19A, 19B, and 19C are graphs illustrating the dependence ofthe permeability μ′, the core loss W_(0.5/200k) and the core lossW_(1/100k), respectively, on the DC magnetic field H of a magneticpowder core;

[0084]FIG. 20 is a circuit diagram of a switching power supply inaccordance with an embodiment of the present invention;

[0085]FIG. 21 is an isometric view of a magnetic powder core of atransformer used in the switching power supply shown in FIG. 20;

[0086]FIG. 22 is a circuit diagram of a switching power supply inaccordance with an embodiment of the present invention.

[0087]FIG. 23 is a circuit diagram of a step-down converter circuit inaccordance with an embodiment of the present invention;

[0088]FIG. 24 is a circuit diagram of a boosting converter circuit inaccordance with an embodiment of the present invention;

[0089]FIG. 25 is a circuit diagram of a polarity-reversing convertercircuit in accordance with an embodiment of the present invention;

[0090]FIG. 26 is a circuit diagram of an active filter in accordancewith an embodiment of the present invention;

[0091]FIG. 27 is an isometric view of an inductor used in a filter inaccordance with an embodiment of the present invention;

[0092]FIG. 28 is a circuit diagram of an amplifying device in accordancewith an embodiment of the present invention;

[0093]FIG. 29 is a graph illustrating a waveform of the input current tothe amplifying device shown in FIG. 27;

[0094]FIG. 30 is a graph illustrating waveforms of input currents to afilter provided in the amplifying device shown in FIG. 27;

[0095]FIG. 31 is a graph illustrating a waveform of an output currentfrom the amplifying device shown in FIG. 27;

[0096]FIG. 32 is an isometric view of a mold used in the production ofinjection-molding articles;

[0097]FIGS. 33A and 33B are schematic views illustrating a method formaking an injection-molding article of an amorphous soft-magnetic alloyof the present invention using the mold shown in FIG. 32.

[0098]FIG. 34 is an isometric view illustrating an injection-moldingarticle and an injection-molding precursor of an amorphous soft-magneticalloy of the present invention using the mold shown in FIG. 32.

[0099]FIG. 35 is a graph illustrating the dependence of the core loss(W) on the frequency of a magnetic powder core of the present inventionand a magnetic powder core for comparison;

[0100]FIG. 36 is a graph illustrating the dependence of the rate ofchange Δμ′ in the amplitude permeability on the magnetic field of amagnetic powder core of the present invention and a magnetic powder corefor comparison;

[0101]FIG. 37 is a graph illustrating X-ray diffraction patterns ofamorphous soft-magnetic alloy tapes in accordance with EXAMPLES 6-1 to6-14;

[0102]FIG. 38 is a graph illustrating DSC thermograms of amorphoussoft-magnetic alloy tapes of EXAMPLES 6-4 and 6-14 and COMPARATIVEEXAMPLE 6;

[0103]FIG. 39 is a ternary diagram illustrating the dependence of theglass transition temperature T_(g) on the P, C, and B contents inamorphous soft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0104]FIG. 40 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the P, C, and B contents inamorphous soft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0105]FIG. 41 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the P, C, and B contents in supercooledliquids of amorphous soft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0106]FIG. 42 is a ternary diagram illustrating the dependence of themelting point T_(m) on the P, C, and B contents in amorphoussoft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0107]FIG. 43 is a ternary diagram illustrating the dependence of theratio T_(g)/T_(m) on the P, C, and B contents in amorphous soft-magneticalloy tapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0108]FIG. 44 is a ternary diagram illustrating the dependence of theCurie temperature T_(c) on the P, C, and B contents in amorphoussoft-magnetic alloy tapes represented byFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0109]FIG. 45 is a ternary diagram illustrating the dependence of thesaturation magnetization δs on the P, C, and B contents in amorphoussoft-magnetic alloy tapes represented byFe₇₀Al₇₍P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0110]FIG. 46 is a ternary diagram illustrating the dependence of thepermeability μe on the P, C, and B contents in amorphous soft-magneticalloy tapes represented by Fe₇₀Al₇(P_(0.7) ₆Si_(0.24))_(v)C_(z)B_(w);

[0111]FIG. 47 is a ternary diagram illustrating the dependence of thecoercive force Hc on the P, C, and B contents in amorphous soft-magneticalloy tapes represented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w);

[0112]FIG. 48 is a graph illustrating X-ray diffraction patterns ofamorphous soft-magnetic alloy tapes in accordance with EXAMPLES 7-15 to7-18;

[0113]FIG. 49 is a ternary diagram illustrating the dependence of theglass transition temperature T_(g) on the Fe and Al contents inamorphous soft-magnetic alloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0114]FIG. 50 is a ternary diagram illustrating the dependence of thecrystallization temperature T_(x) on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0115]FIG. 51 is a ternary diagram illustrating the dependence of thetemperature difference ΔT_(x) on the Fe and Al contents in supercooledliquids of amorphous soft-magnetic alloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0116]FIG. 52 is a ternary diagram illustrating the dependence of themelting point T_(m) on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0117]FIG. 53 is a ternary diagram illustrating the dependence of theratio T_(g)/T_(m) on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0118]FIG. 54 is a ternary diagram illustrating the dependence of theCurie temperature T_(c) on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0119]FIG. 55 is a ternary diagram illustrating the dependence of thesaturation magnetization δs on the Fe and Al contents in amorphoussoft-magnetic alloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0120]FIG. 56 is a ternary diagram illustrating the dependence of thepermeability μe on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0121]FIG. 57 is a ternary diagram illustrating the dependence of thecoercive force Hc on the Fe and Al contents in amorphous soft-magneticalloy tapes represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)Si_(0.13) )_(y);

[0122]FIG. 58 is a graph illustrating an X-ray diffraction pattern of aninjection-molding article in accordance with EXAMPLE 8-19;

[0123]FIG. 59 is a DSC thermogram of the injection-molding article inaccordance with EXAMPLE 8-19;

[0124]FIG. 60 is a graph illustrating a B-H curve of aninjection-molding article before annealing in accordance with EXAMPLE8-19;

[0125]FIG. 61 is a graph illustrating a B-H curve of theinjection-molding article after annealing in accordance with EXAMPLE8-19;

[0126]FIG. 62 is a graph illustrating a B-H curve of aninjection-molding article before annealing in accordance withCOMPARATIVE EXAMPLE 2; and

[0127]FIG. 63 is a graph illustrating a B-H curve of theinjection-molding article after annealing in accordance with COMPARATIVEEXAMPLE 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0128] Preferred embodiments of a magnetic powder core and a method formaking the same in accordance with the present invention will nowdescribed with reference to the drawings.

[0129] The magnetic powder core comprises a molded article of a mixtureof a glassy alloy powder and an insulating material, the glassy alloycomprises Fe and at least one element Q selected from Al, P, C, Si, andB, has a texture primarily composed of an amorphous phase, and has atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature. Preferably, the glassy alloy has aresistivity of at least 1.5 μΩ•m.

[0130]FIG. 1 shows a toroidal magnetic powder core 1. The magneticpowder core 1, however, may have any other shape, e.g., an ellipsoidalring, an oval ring, an E shape, a U shape, or an I shape.

[0131] In the texture constituting the magnetic powder core, the glassyalloy powder is dispersed in the insulating material. Thus, the glassyalloy powder does not form a homogeneous texture which can be formed bythe melt of the glassy alloy. Preferably, individual particles areinsulated from each other in the matrix of the insulating material.Thus, the magnetic powder core has large resistivity, reduced eddycurrent loss, and a moderated reduction in permeability in ahigh-frequency region.

[0132] When the temperature difference ΔT_(x) in the supercooled liquidof the glassy alloy is less than 20 K, it is difficult to adequatelyrelieve the internal stress without crystallization at an annealingtreatment after the compaction molding of the mixture of the glassyalloy powder and the insulating material. When the temperaturedifference ΔT_(x) is at least 20 K, the annealing can be performed at alower temperature which does not cause excess decomposition of theinsulating layer and increased loss.

[0133] In the magnetic powder core of the present invention, themagnetic powder has a coercive force of preferably 80 A/m or less andmore preferably 40 A/m or less in an applied magnetic field of ±2.4kA/m.

[0134] The insulating material enhances resistivity of the magneticpowder core and maintains the shape of the magnetic powder core bybinding the glassy alloy powder. Insulating materials which do not causelarge loss in magnetic properties are preferred. Examples of suchinsulating materials include liquid or powdered organic compounds, e.g.,epoxy resins, silicone resins, phenolic resins, urea resins, melamineresins, and polyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂;oxide glass powders, e.g., Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂, and TiO₂.

[0135] The insulating material may be any elastomer, for example, asilicone rubber. The insulating material may be used together with astearate salt as a lubricant. Examples of stearate salts include zincstearate, calcium stearate, barium stearate, magnesium stearate, andaluminum stearate.

[0136] The glassy alloy powder constituting the magnetic powder core ofthe present invention is prepared by pulverizing a tape of a glassyalloy having the above-mentioned composition, texture, and properties,by atomizing the melt of the glassy alloy onto a rotating coolingroller, by atomizing and cooling the melt of the glassy alloy with ahigh-pressure gas, or by atomizing the melt of the glassy alloy intowater. Since the glassy alloy powder has a texture primarily composed ofan amorphous phase, it exhibits superior soft magnetic characteristics,such as low coercive force.

[0137] In particular, the powder prepared by atomizing and cooling themelt of the glassy alloy with a high-pressure gas has higher sphericitycompared with the powders prepared by the other processes, resulting inhigh processability and moldability. Accordingly, this powder issuitable for the magnetic powder core of the present invention.

[0138] The glassy alloy has a large temperature difference ΔT_(x) of 40K or more and particularly 50 K or more, and has a large resistivity ofat least 1.5 μΩ•m in optimized compositions. These properties are notobtainable from conventional alloys. Moreover, the glassy alloy of thepresent invention exhibits the superior soft magnetic characteristics atroom temperature, unlike conventional alloys.

[0139] In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

[0140] In the glassy alloy having a large temperature difference ΔT_(x),the atomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over a broad temperature range. Since theglassy alloy of the present invention has a large temperature differenceΔT_(x) in a supercooled liquid, the alloy is readily supercooled to aglass transition temperature T_(g) below the crystallization temperatureT_(x) without being crystallized during a cooling step of the melt,readily forming an amorphous phase.

[0141] Thus, the amorphous phase can be formed at a relatively lowcooling rate. For example, a glassy alloy powder primarily composed ofan amorphous phase is obtainable by pulverizing a bulk glassy alloy,which is prepared by a casting process, in addition to liquid quenchingprocesses having relatively high cooling rates, such as a single-rollerprocess.

[0142] The glassy alloy preferably used in the magnetic powder core ofthe present invention contains, for example, iron (Fe) as the majorcomponent, aluminum (Al), and at least one element Q selected from P, B,C, and Si. Preferably, the glassy alloy contains all of P, B, C, and Sirepresented by the element Q.

[0143] The glassy alloy may be represented by the following formula:

(Fe_(1-a)T_(a))_(100-x-v-z-w)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w)

[0144] wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent.

[0145] Preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.35 byatomic ratio, 0 atomic percent<x≦15 atomic percent, 8 atomicpercent<v≦18 atomic percent, 0.5 atomic percent≦z≦7.4 atomic percent,and 3 atomic percent≦w≦14 atomic percent. More preferably, thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0.1 by atomic ratio≦b≦0.28 by atomic ratio, 0 atomicpercent<x≦10 atomic percent, 11.3 atomic percent<v≦14 atomic percent,1.8 atomic percent≦z≦4.6 atomic percent, and 5.3 atomic percent≦w≦8.6atomic percent.

[0146] Fe—Al—Ga—C—P—Si—B glassy alloys are known. These glassy alloyscontain iron (Fe) and other elements which facilitate the formation ofan amorphous phase, such as aluminum (Al), gallium (Ga), carbon (C),phosphorus (P), silicon (Si), and boron (B).

[0147] On the other hand, the glassy alloy of the present inventioncontains Fe, Al, and at least one element Q selected from P, B, C, andSi. That is, the glassy alloy of the present invention does not containGa, but does contain an increased amount of Al. Thus, the presentinvention is characterized in that the glassy alloy of the presentinvention can contain an amorphous phase regardless of the omission ofGa, which has been considered to be an essential element for theformation of the amorphous layer, and that this glassy alloy has a largetemperature difference ΔT_(x) in a supercooled liquid. These facts havebeen discovered by the present inventors.

[0148] Aluminum (Al) is an essential element for the amorphoussoft-magnetic alloy. At an Al content x of 20 atomic percent or less,this alloy has a perfect amorphous phase due to extremely enhancedamorphous formability of Al, and the amorphous soft-magnetic alloy has atemperature difference ΔT_(x) of 20 K or more in a supercooled liquid.

[0149] Since Al has a negative enthalpy of mixing with Fe and has anatomic radius which is larger than that of Fe, a combined use of Al withP, B, and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

[0150] The Al content x is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

[0151] Iron (Fe) is essential for the glassy alloy of the presentinvention as a magnetic element. In the present invention, Fe may bepartially replaced with at least one element T selected from Co and Ni.A higher Fe content contributes to improved saturation magnetization ofthe resulting glassy alloy.

[0152] Carbon (C), phosphorus (P), silicon (Si), and boron (B)contribute to the formation of an amorphous phase. A multicomponentsystem containing Fe, Al, and these elements facilitates the formationof a more stable amorphous phase, compared with an Fe—Al binary system.

[0153] In particular, phosphorus (P) having high amorphous formabilityfacilitates the formation of a perfect amorphous phase over the entiretexture of the glassy alloy and ensures an adequate temperaturedifference ΔT_(x) in a supercooled liquid. Combined addition ofphosphorus and silicon causes a further increased temperature differenceΔT_(x) in a supercooled liquid.

[0154] When both phosphorus and silicon are added in combination, thetotal content v of the phosphorus and silicon is preferably more than 0to 22 atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

[0155] The subscript b representing the relative Si and P contents byatomic ratio is preferably in the range of 0<b≦0.8 when 0 atomicpercent<v≦22 atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v≦18atomic percent, or 0.1≦b≦0.28 when 11.3 atomic percent≦v≦14 atomicpercent.

[0156] When the subscript b exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

[0157] Herein, the Si content in the glassy alloy is in the range ofpreferably 17.6 atomic percent or less, more preferably 0.8 to 6.3atomic percent, and most preferably 1.13 to 3.92 atomic percent.

[0158] The above-mentioned ranges for the subscripts b and vrepresenting the P and Si contents, respectively, contribute to anincreased temperature difference ΔT_(x) in a supercooled liquid.

[0159] The subscript z representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

[0160] The subscript w representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

[0161] The glassy alloy may contain 4 atomic percent or less Ge, and 0to 7 atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

[0162] The glassy alloy of the present invention has a temperaturedifference ΔT_(x) of at least 20 K in the above-described composition,at least 35 K in a particular composition, or at least 50 K in anoptimized composition.

[0163] The glassy alloy of the present invention may contain otherincidental impurities.

[0164] An embodiment of a method for making the magnetic powder core inaccordance with the present invention will now be described withreference to the drawings.

[0165] The method for making the magnetic powder core includes a powderpreparation step of preparing a powder of a glassy alloy comprising Feand at least one element Q selected from Al, P, C, Si, and B, having atexture primarily composed of an amorphous phase, and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature, a molding step of mixing the glassy alloypowder with an insulating material and compacting the mixture to form amagnetic core precursor, and an annealing step of annealing the magneticcore precursor at a temperature in the range between (T_(g)−170) K andT_(g) K to relieve the internal stress of the magnetic core precursor.

[0166] In the powder preparation step, for example, a glassy alloypowder is prepared by pulverizing a glassy alloy tape and thenclassifying the particles.

[0167] The glassy alloy tape is produced by a roller quenching processin which the melt of the glassy alloy is jetted onto a cold rotatingroller so that the melt is quenched. The glassy alloy tape may bepulverized using a rotor mill, a ball mill, a jet mill, an atomizer, ora grinding mill.

[0168] The trituration is classified to select particles having apredetermined average particle size. The average particle size of thepowder is preferably 30 μm or more and more preferably 45 μm to 300 μm.At an average particle size of less than 30 μm, particles may becontaminated by a rotor mill or the like during pulverizing. At anaverage particle size exceeding 300 μm, relatively large particles maycause the formation of voids in the magnetic powder core in a compactionmolding process of a mixture of the powder and an insulating material,resulting in undesirably large coercive force. The classification of thetrituration may be performed using a screen, a vibrating screen, anultrasonic screen, or an air-flow classifier.

[0169] In another embodiment of the powder preparation step, the mist ofthe glassy alloy melt having the above-mentioned composition is sprayedonto a rotating cooling roller. In this process, glassy alloy powder iseasily obtained. The average particle size of the powder is determinedby controlling the rotation rate of the cooling roller, the temperatureof the melt, and spraying conditions.

[0170] The glassy alloy powder is also prepared by a gas atomizingprocess, which involves atomizing a glassy alloy melt with a highpressure gas into a gaseous atmosphere for cooling, or by an aqueousatomizing process, which involves atomizing a glassy alloy melt intowater for cooling.

[0171] In the gas atomizing process, a crucible with a jet nozzle isfilled with the glassy alloy melt maintained at a temperature which isat least 140° C. higher than the melting point of the glassy alloy, andthe melt is atomized with an inert gas, such as nitrogen or argon, of apressure of at least 5.9 MPa. The gaseous atmosphere is preferably aninert gas atmosphere of, for example, argon or nitrogen, in order toprevent oxidation of the alloy.

[0172] The atomized melt is instantaneously cooled and is converted intosubstantially spherical particles having a texture primarily composed ofan amorphous phase. In particular, the glassy alloy of the presentinvention containing Fe, Al, and at least one element Q selected from P,B, C, and Si exhibits high formability of an amorphous phase. Thus, anamorphous alloy can be produced by a gas atomizing process, which is notapplicable to conventional FeSiB-based alloys.

[0173] The average particle size of the glassy alloy powder prepared bya gas atomizing process is preferably in the range of 2 to 100 μm andmore preferably 2 to 60 μm. An average particle size of less than 2 μmdecreases the density of the compact, and the magnetic powder core has adecreased saturation magnetic flux density, a decreased permeability, anincreased coercive force, and an increased core loss. An averageparticle size exceeding 100 μm may cause the formation of voids in themagnetic powder core during compaction molding of a mixture of theglassy alloy powder and an insulating material, resulting in increasedcoercive force. Moreover, these particles have reduced cooling rates. Asa result, the amorphous phase has a decreased volume fraction in thetexture.

[0174] It is preferable that the average particle size of the resultingpowder be precisely controlled using a screen, a vibrating screen, anultrasonic screen, or an air-flow classifier, although the averageparticle size is controllable to some extent by the temperature of themelt and the gas pressure during the spraying operation.

[0175] In the subsequent molding step, the glassy alloy powder is mixedwith the above-mentioned insulating material, and the mixture iscompacted to form a magnetic core precursor. The content of theinsulating material is preferably 0.3 weight percent to 5 weight percentand more preferably 1 weight percent to 5 weight percent in the mixture.An insulating material content of less than 0.3 weight percent precludesmolding of the mixture into a predetermined shape. An insulatingmaterial content exceeding 5 weight percent causes deterioration of thesoft magnetic characteristics of the magnetic powder core due to adecreased glassy alloy content in the magnetic powder core. Prior to thecompaction molding, the solvents and moisture contained in the mixtureare preferably removed by evaporation so as to form an insulating layeron the surface of the glassy alloy powder.

[0176] Next, the mixture is compacted to form a magnetic core precursor,using a mold 10 shown in FIG. 2. The mold 10 substantially consists of ahollow cylindrical die 11, an upper punch 12, and a lower punch 13. Theupper punch 12 and the lower punch 13 will be inserted into a hollowsection 11 a of the hollow cylindrical die 11. The upper punch 12 has acylindrical protrusion 12 a on the bottom face thereof. An assembly ofthe upper punch 12, the lower punch 13, and the hollow cylindrical die11 forms a toroidal mold in the interior of the mold 10. The toroidalmold is filled with the above-mentioned mixture.

[0177] The mixture is heated to a predetermined temperature in the mold10 while applying a unidirectional pressure to compact the mixture.

[0178]FIG. 3 is a schematic cross-sectional view of a discharge plasmasintering apparatus which is suitable for compaction molding. Thedischarge plasma sintering apparatus has the mold 10 filled with themixture, a lower punch electrode 14, an upper punch electrode 15, and athermocouple 17 for measuring the temperature of the mixture in the mold10. The lower punch electrode 14 supports the lower punch 13 andfunctions as an electrode for applying a pulsed current, whereas theupper punch electrode 15 compresses the upper punch 12 downwardly andfunctions as another electrode for the pulsed current.

[0179] The discharge plasma sintering apparatus is placed in a chamber18 which is connected to a vacuum pumping system and an atmospheric gassupplying system (both are not shown in the drawing) so that the mixtureloaded into the mold 10 is placed in a desired atmosphere, such as aninert gas atmosphere.

[0180] The lower punch electrode 14 and the upper punch electrode 15 areconnected to an energizing system (not shown in the drawing) so as tosupply electrical power between the lower punch 13 and the upper punch12.

[0181] The mold 10 filled with the mixture is placed into the dischargeplasma sintering apparatus, and the apparatus is evacuated while themixture is heated by a pulsed current applied to the upper punch 12 andthe lower punch 13 under a unidirectional pressure P applied between theupper punch 12 and the lower punch 13, to complete compaction molding.

[0182] Since the applied pulsed current can rapidly heat the mixture toa predetermined temperature in the discharge plasma sintering apparatus,the glassy alloy can be compacted within a short molding time withoutdeterioration of the amorphous phase.

[0183] The temperature during the compaction molding depends on the typeof the insulating material and the composition of the glassy alloy. In acombination of a liquid-glass insulating material and a glassy alloytape having a composition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, thetemperature must be 373 K (100° C.) or more so that the glassy alloyparticles are bonded to each other in the matrix of the insulatingmaterial, and must be 673 K (400° C.) or less so that the meltedinsulating material does not ooze from the mold 10. If the insulatingmaterial oozes from the mold 10, the magnetic powder core has decreasedresistivity due to a decreased insulating material content, resulting indecreased permeability in a high-frequency region.

[0184] When the mixture is compacted at a temperature between 373 K(100° C.) and 673 K (400° C.), the insulating material is moderatelysoftened so that the glassy alloy particles are bonded to each other andthe mixture is maintained to a desired shape.

[0185] In compaction molding under a significantly low unidirectionalpressure P, the density of the magnetic powder core is not increased,that is, the magnetic powder core is not dense. Under a high pressure P,the insulating material oozes out, and the insulating material contentin the magnetic powder core decreases, resulting in decrease inresistivity and permeability in a high-frequency region. A preferredunidirectional pressure P is determined by the type of the insulatingmaterial and the composition of the glassy alloy. In a combination of aliquid-glass insulating material and a glassy alloy tape having acomposition of Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, the unidirectionalpressure P is in the range of preferably 600 MPa to 1,500 MPa and morepreferably 600 MPa to 900 MPa. A toroidal magnetic core precursor isprepared in such a manner.

[0186] When a silicone rubber is used as the insulating material, amixture of the glassy alloy powder and the silicone rubber can becompacted at room temperature in the above molding process to obtain amagnetic core precursor having a predetermined shape.

[0187] Since the silicone rubber has elasticity, the glassy alloy powderexhibits small hardening stress and small internal residual stress.Thus, the resulting glassy alloy exhibits improved soft magneticcharacteristics without the affection by magnetostriction. As a result,the magnetic powder core exhibits significantly improved coercive forceand core loss.

[0188] This magnetic powder core exhibits a core loss of 400 kW/m³ orless at a frequency of 100 kHz and a magnetic flux density of 0.1 T.This value is significantly smaller than that of a conventional magneticpowder core.

[0189] When a significantly low pressure is applied to the mixtureduring the compaction molding using the silicone rubber, the resultingmagnetic powder core is not dense. When a significantly high pressure isapplied, the silicone rubber oozes out, resulting in a decreasedsilicone rubber content in the magnetic powder core, and the resistivityof the magnetic powder core is decreased, resulting in decreasedpermeability at a high-frequency region. The preferred pressure dependson the composition of the glassy alloy. When a glassy alloy having acomposition of Fe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87) is used, thepressure is in the range of preferably 500 MPa to 2,500 MPa and morepreferably 1,000 MPa to 2,000 MPa.

[0190] Next, an annealing step is performed for annealing the magneticcore precursor to relieve the internal stress thereof. The internalstress occurs in the magnetic core precursor and the glassy alloy powderduring the powder preparation step and the molding step. The stress isrelieved by annealing the magnetic core precursor within a predeterminedtemperature difference. The resulting magnetic powder core exhibits lowcoercive force.

[0191] The annealing temperature is in the range of desirably(T_(g)−170) K to (T_(g)) K, preferably (T_(g)−160) K to (T_(g)−50) K,more preferably (T_(g)−140) K to (T_(g)−60) K, and (T₉−110) K to(T_(g)−60) K.

[0192] When the magnetic core precursor is annealed at a temperaturebetween (T_(g)−160) K and (T_(g)−50), the magnetic powder core has acoercive force of 100 A/m or less at an applied magnetic field of ±2.4kA/m. When the magnetic core precursor is annealed at a temperaturebetween (T_(g)−140) K and (T_(g)−60), the magnetic powder core has acoercive force of 80 A/m or less at an applied magnetic field of ±2.4kA/m. In addition, when the magnetic core precursor is annealed at atemperature between (T_(g)−110) K and (T_(g)−60), the magnetic powdercore has a coercive force of 40 A/m or less at an applied magnetic fieldof ±2.4 kA/m.

[0193] At an annealing temperature of less than (T_(g)−170) K, theinternal stress in the magnetic core precursor is not sufficientlyrelieved. At an annealing temperature exceeding (T_(g)) K, the alloyexhibits high coercive force due to crystallization.

[0194] For example, in the case of a glassy alloy having a compositionof Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃, the annealing temperature is inthe range of desirably 573 K (300° C.) to 723 K (450° C.), preferably603 K (330° C.) to 713 K (440° C.), more preferably 623 K (350° C.) to703 K (430° C.), and most preferably 653 K (380° C.) to 703 K (430° C.).

[0195] When a silicone rubber is used as the insulating material, theannealing temperature is preferably in the range of 653 K (380° C.) to703 K (430° C.). At an annealing temperature-of less than 653 K, theinternal stress in the magnetic core precursor is insufficientlyrelieved. At an annealing temperature exceeding 703 K, the siliconerubber is significantly decomposed, resulting in decreased mechanicalstrength of the magnetic powder core. The silicone rubber is preferablyannealed in vacuum or in an inert gas atmosphere, such as a nitrogenatmosphere or an argon atmosphere. The nitrogen gas atmosphere is morepreferable.

[0196] A toroidal magnetic powder core is formed by such annealing.

[0197] The resulting magnetic powder core containing the glassy alloypowder exhibits superior soft magnetic characteristics at roomtemperature and the soft magnetic characteristics are further improvedby annealing. This magnetic powder core is applicable to magnetic coresof various magnetic elements which require superior soft magneticcharacteristics.

[0198] In addition to the above-described compaction molding in thedischarge plasma sintering apparatus, the mixture of the glassy alloypowder and the insulating material may be compacted by conventionalpowder molding, hot pressing, or extruding.

[0199] In this embodiment, the toroidal magnetic powder core ismanufactured using a mold. In an alternative embodiment, a bulk compactis prepared and is cut into various shapes, e.g., toroidal shapes, rods,E shapes, and U shapes. Magnetic powder cores having desired shapes canalso be prepared in such a manner.

[0200] The magnetic powder core is formed of a mixture of theabove-mentioned glassy alloy powder and the above-mentioned insulatingmaterial. The insulating material contributes to increased resistivityof the entire magnetic powder core and reduced core loss due todecreased eddy current loss in the magnetic powder core withoutdecreased permeability in a high-frequency region.

[0201] When a glassy alloy having a resistivity of at least 1.5 μΩ•m isused, the resulting magnetic powder core shows further reduced core lossdue to reduced eddy current loss in the glassy alloy particles in ahigh-frequency region.

[0202] Since the magnetic core precursor is annealed at a temperaturebetween (T_(g)−170) K and (T_(g)) K in this embodiment, the internalstress in the glassy alloy or the magnetic core precursor is relievedwithout crystallization of the glassy alloy. Thus, the magnetic powdercore exhibits low coercive force.

[0203] A glassy alloy powder prepared by an atomizing process using gasis composed of spherical particles having a small average particle size.A magnetic powder core using this glassy alloy powder exhibits low coreloss, a high rate of change in permeability to a change in an appliedmagnetic field (amplitude permeability), and a high rate of change ininductance to a change in an applied magnetic field (DC-superimposingcharacteristic).

[0204] The silicone rubber as the insulating material does not requireheating during compaction molding and can significantly reduce theinternal stress in the magnetic powder core. Thus, the magnetic powdercore exhibits significantly reduced coercive force and core loss.

[0205]FIG. 20 shows an exemplary switching power supply 20 in accordancewith the present invention. This switching power supply 20 includes aswitching element 22, a transformer 23, a rectification circuit 24, anda smoothing circuit 25.

[0206] The switching element 22 consists of, for example, a switchingtransistor and converts a DC voltage from a DC power source 26 into arectangular pulsed current in response to a drive signal input through abase terminal.

[0207] The transformer 23 includes a magnetic core composed of theglassy alloy of the present invention. One input terminal is connectedto the DC power source 26, whereas the other is connected to theswitching element 22. The transformer 23 transforms the rectangularpulsed voltage from the switching element 22.

[0208] The rectification circuit 24 consists of, for example, a diodeand is connected to one output terminal.

[0209] The smoothing circuit 25 consists of, for example, a capacitorand is connected to the output terminals of the transformer 23 inparallel.

[0210] The rectification circuit 24 and the smoothing circuit 25 convertthe rectangular pulsed voltage, which is transformed in the transformer23, into a DC voltage Vout1 which is output through output terminals.

[0211] The magnetic core constituting the transformer 23 is a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x) T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.

[0212] Preferably, the glassy alloy has a resistivity of at least 1.5μΩ•m.

[0213] This magnetic core has low core loss and a low permeability inthe range of 100 to 300 at a frequency of 100 kHz.

[0214] An exemplary shape of the magnetic core 30 is toroidal as shownin FIG. 21. The magnetic core may have any other shape, for example, anellipsoidal or oval ring. Alternatively, the magnetic core may havesubstantially an E shape, a U shape, or an I shape, in a plan view.

[0215] The magnetic core 30 is formed of a glassy alloy powder which hasa composition described below and is present in a texture of aninsulating material. This texture is not homogeneous, since the powderof the glassy alloy is not dissolved into the matrix. It is preferablethat the glassy alloy particles be insulated from each other by theinsulating material.

[0216] The insulating material increases the resistivity of the magneticcore 30, resulting in decreased core loss due to reduced eddy currentloss.

[0217] At a temperature difference ΔT_(x) of less than 20 K in thesupercooled liquid of the glassy alloy, the glassy alloy will beinevitably crystallized during annealing for relieving the internalstress. At a temperature difference ΔT_(x) exceeding 20 K, the internalstress can be adequately relieved without loss due to decomposition ofthe insulating material at a reduced temperature.

[0218] Since the glassy alloy having a specific composition has atemperature difference ΔT_(x) of 60 K or more, the internal stress inthe magnetic core 30 can be adequately relieved during annealing. Thus,the magnetic core 30 exhibits improved soft magnetic characteristicswithout loss due to deterioration of the insulating material duringannealing at a reduced temperature. Moreover, the magnetic core 30exhibits low core loss due to relaxation of the internal stress.

[0219] Since the magnetic core 30 has a permeability in theabove-described range, the magnetic core 30 does not require a gap forpreventing saturation of the magnetic flux. Thus, no leakage magneticfield is generated.

[0220] It is preferable to use an insulating material which enhances theresistivity of the magnetic core 30, which binds the glassy alloyparticles so as to maintain the shape of the magnetic core 30, and whichdo not cause large loss of magnetic characteristics. Examples of suchinsulating materials include liquid or powdered organic compounds, e.g.,epoxy resins, silicone resins, phenolic resins, urea resins, melamineresins, and polyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂;oxide glass powders, e.g.. Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂, and TiO₂.

[0221] The insulating material may be used together with a stearate saltas a lubricant. Examples of stearate salts include zinc stearate,calcium stearate, barium stearate, magnesium stearate, and aluminumstearate.

[0222] The glassy alloy powder contains a primary phase having aresistivity of at least 1.5 μ•Ω and a temperature difference ΔT_(x) ofat least 20 K in a supercooled liquid. The glassy alloy powder isprepared by atomizing the melt of the glassy alloy onto a coolingroller, by atomizing the melt of the glassy alloy together with apressurized gas into the atmosphere, or by atomizing the melt of theglassy alloy into water. The resulting glassy alloy powder exhibits lowcore loss and superior soft magnetic characteristics.

[0223] In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

[0224] In the glassy alloy having a large temperature difference ΔT_(x),the atomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over the large temperature difference.

[0225] Thus, the glassy alloy can have an adequate amorphous phase by arelatively low cooling rate. The glassy alloy primarily composed of theamorphous phase can be prepared, for example, by a liquid quenchingprocess having a relatively low cooling rate, such as a single rollerprocess, or by pulverizing a bulk glassy alloy prepared by a castingmethod.

[0226] The switching power supply 20 has the transformer 23 includingthe magnetic core 30 composed of the glassy alloy powder. The internalstress of the magnetic core 30 can be relieved by annealing at atemperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theentire switching power supply 20 can be reduced.

[0227] The magnetic core 30 exhibiting low permeability does not requirea gap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0228]FIG. 22 shows a switching power supply as an embodiment of thepresent invention. The switching power supply 31 includes a switchingelement 32, a transformer 33, a rectification circuit 34, and asmoothing circuit 35.

[0229] The switching element 32 consists of, for example, a switchingtransistor and converts a DC voltage from a DC power source 36 into arectangular pulsed current in response to a drive signal input through abase terminal.

[0230] One input terminal is connected to the DC power source 36,whereas the other terminal is connected to the switching element 32. Thetransformer 33 transforms the rectangular pulsed voltage from theswitching element 32.

[0231] The rectification circuit 34 consists of, for example, a pair ofdiodes 34 a and is connected to the output side of the transformer 33.The diode 34 a is connected in the backward direction with respect tothe other diode 34 b in the circuit.

[0232] The smoothing circuit 35 consists of, for example, a capacitor 35a and a coil 35 b with a magnetic core and is connected to therectification circuit 34.

[0233] The rectification circuit 34 and the smoothing circuit 35 convertthe rectangular pulsed voltage, which is transformed in the transformer33, into a DC voltage Vout2 which is output through output terminals.

[0234] As in the above embodiment, the magnetic core of the coil 35 is amolded article of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.

[0235] This magnetic core has low core loss and a low permeability inthe range of 100 to 300 at a frequency of 100 kHz, as in theabove-described magnetic core 30.

[0236] The switching power supply 31 includes the coil 35 b with themagnetic core composed of the glassy alloy powder. The internal stressof the magnetic core can be relieved by annealing at a temperature whichis sufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire switching power supply11 can be reduced.

[0237] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0238]FIG. 23 shows a step-down converter circuit as an embodiment ofthe present invention. The step-down converter circuit 41 includes aswitching element 42, a coil 43 with a magnetic core, a rectificationelement 44, and a capacitor 45.

[0239] The switching element 42 consists of, for example, a switchingtransistor, and intermittently interrupts the DC voltage Vin3, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

[0240] The coil 43 with the magnetic core is connected in series to theswitching element 42. As in the above magnetic core 30, the magneticcore of the coil 43 is a molded article of a mixture of a glassy alloypowder and an insulating material, and the glassy alloy powder has atexture primarily composed of an amorphous phase and has a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0241] Thus, this magnetic core also has low core loss and a lowpermeability in the range of 100 to 300 at a frequency of 100 kHz, as inthe above-described magnetic core 30.

[0242] The rectification element 44 consists of, for example, a diodeand is connected in the backward direction with respect to the switchingelement 42 and in parallel to the coil 43 with the magnetic core. Thecapacitor 45 is connected in parallel to an external load.

[0243] The coil 43 with the magnetic core, the rectification element 44,and the capacitor 45 form a circulating current path. Thus, therectification element 44 functions as a circulating current diode.

[0244] When the switching element 42 is closed, a DC voltage(Vin3−Vout3) is generated in the coil 43. When the switching element 42is opened, the coil 43 generates a counterelectromotive force whichcauses a circulating current flow in the capacitor 45 and therectification element 44.

[0245] When the open-close operations of the switching element 42 arerepeated, the pulsed voltage are smoothed by the coil 43 with themagnetic core and the capacitor 45 so that a DC voltage Vout3(Vin3>Vout3) is output through the output terminals.

[0246] In the step-down converter circuit 41, the magnetic core of thecoil 43 is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire step-down convertercircuit 41 can be reduced.

[0247] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0248]FIG. 24 shows a boosting converter circuit as an embodiment of thepresent invention. The boosting converter circuit 51 includes aswitching element 52, a coil 53 with a magnetic core, a rectificationelement 54, and a capacitor 55.

[0249] The switching element 52 consists of, for example, a switchingtransistor, and intermittently interrupts the DC voltage Vin4, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

[0250] The coil 53 with the magnetic core is connected in series to theswitching element 52. As in the above magnetic core, the magnetic coreof the coil 53 is a molded article of a mixture of a glassy alloy powderand an insulating material, and the glassy alloy powder has a textureprimarily composed of an amorphous phase and has a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0251] Thus, this magnetic core also has low core loss and a lowpermeability in the range of 100 to 300 at a frequency of 100 kHz, as inthe above-described magnetic core.

[0252] The rectification element 54 consists of, for example, a diodeand is connected in series to the coil 53 with the magnetic core and inparallel to the switching element 52. The capacitor 45 is connected inparallel to an external load.

[0253] When the switching element 52 is closed, a DC voltage Vin4 isgenerated in the coil 53. In this mode, both input terminals areshort-circuited and no currents flow in the output side.

[0254] When the switching element 52 is opened, the coil 53 generates acounterelectromotive force and a current flows in the rectificationelement 54.

[0255] When the open-close operations of the switching element 42 arerepeated; a current due to the counterelectromotive force intermittentlyflows in the rectification element 54, and the intermittent current issmoothed by the capacitor 55 so that a DC voltage Vout4 (Vin4>Vout4) isoutput through the output terminals.

[0256] In the step-down converter circuit 51, the magnetic core of thecoil 53 is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire boosting convertercircuit 51 can be reduced.

[0257] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0258]FIG. 25 shows a polarity-reversing converter circuit as anembodiment of the present invention. The polarity-reversing convertercircuit 61 includes a switching element 62, a coil 63 with a magneticcore, a rectification element 64, and a capacitor 65.

[0259] The switching element 62 consists of, for example, a switchingtransistor, intermittently interrupts the DC voltage Vin5, which isinput from the input terminal side, in response to a drive signal inputthrough a base terminal, and converts the voltage into a intermittent,rectangular pulsed current.

[0260] The coil 63 with the magnetic core is connected in series to theswitching element 62. The magnetic core of the coil 63 is also a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, and the glassy alloy powder has a texture primarily composedof an amorphous phase and has a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.

[0261] Thus, this magnetic core also has low core loss and a lowpermeability in the range of 100 to 300 at a frequency of 100 kHz, as inthe above-described magnetic core.

[0262] The rectification element 64 consists of, for example, a diodeand is connected in the backward direction in series to the switchingelement 62. The capacitor 65 is connected in parallel to an externalload.

[0263] When the switching element 62 is closed, a current i1 generatedby a DC voltage Vin5 flows in the coil 63. Since the rectificationelement 44 is connected backward to the switching element 42, nocurrents flow in the output side.

[0264] When the switching element 62 is opened, the coil 63 generates acounterelectromotive force and a current i2 flows in the capacitor 65.

[0265] When the open-close operations of the switching element 62 arerepeated, a current i2 due to the counterelectromotive forceintermittently flows in the capacitor 65 so that a DC voltage −Vout5 isgenerated between the both terminals of the capacitor 65.

[0266] The DC voltage Vin5 having a positive polarity is output as a DCvoltage Vout5 having a negative polarity through the output terminals.

[0267] In the step-down converter circuit 61, the magnetic core of thecoil 63 is composed of a glassy alloy powder. The internal stress of themagnetic core can be relieved by annealing at a temperature which issufficiently lower than the crystallization temperature of the glassyalloy, and the heat dissipation from the entire polarity-reversingconverter circuit 61 can be reduced.

[0268] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0269]FIG. 26 shows an active filter as an embodiment of the presentinvention. The active filter 71 is called a boosting PWM-type activefilter, and includes a control unit 72, a start circuit 73, arectification circuit 74, a noise filter circuit 75, and the boostingconverter circuit 51 described in the former embodiment.

[0270] The control unit 72 is, for example, an active filter monolithicIC having an oscillator, a controlling amplifier, a multiplier, and acurrent detector, and controls the switching interval of the switchingelement 52 in the boosting converter circuit 51.

[0271] The start circuit 73 detects a current flowing in the coil 53with the magnetic core and controls the switching interval of theswitching element 52 in the boosting converter circuit 51 to control therush current when a voltage is input.

[0272] The rectification circuit 74 converts the AC voltage from theinput side into a pulsating flow, while the noise filter circuit 75removes noise generated by the boosting converter circuit 51.

[0273] The boosting converter circuit 51 includes, as described above,the boosting converter circuit 51, the coil 53 with the magnetic core,the rectification element 54, and the capacitor 55.

[0274] The pulsating flow from the rectification circuit 74 is appliedto the switching element 52 when the switching element 52 is closed.When the switching element 52 is opened, a counterelectromotive force isgenerated in the coil 53 with the magnetic core so that a current flowsin the rectification element 54.

[0275] The control unit 72 controls the open-close operations of theswitching element 52. When the open-close operations of the switchingelement 52 are repeated, a current due to the counterelectromotive forceintermittently flows in the rectification circuit 34, and this currentis smoothed by the capacitor 55 so that a DC voltage is output throughthe output terminals. Since this circuit does not require a smoothingcircuit at the input side, the input current does not include harmonicdistortion.

[0276] The magnetic core of the coil 53 is also a molded article of amixture of a glassy alloy powder and an insulating material, and theglassy alloy powder has a texture primarily composed of an amorphousphase and has a temperature difference ΔT_(x), which is represented bythe equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooledliquid, wherein T_(x) indicates the crystallization temperature andT_(g) indicates the glass transition temperature.

[0277] Thus, this magnetic core also has low core loss and a lowpermeability in the range of 100 to 300 at a frequency of 100 kHz, as inthe above-described magnetic core.

[0278] In the active filter 71, the magnetic core of the coil 53 iscomposed of a glassy alloy powder. The internal stress of the magneticcore can be relieved by annealing at a temperature which is sufficientlylower than the crystallization temperature of the glassy alloy, and theheat dissipation from the entire active filter 71 can be reduced.

[0279] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation and does not generate a leakagemagnetic field which adversely affects the other peripheral circuits.

[0280] The composition of the glassy alloy in accordance with thepresent invention will now be described in detail.

[0281] The glassy alloy used in the magnetic core is primarily composedof Fe, and contains Al and the element Q. The element Q may not includeSi.

[0282] The glassy alloy is represented by, for example, the followingformula:

(Fe_(1-a2)T_(a2))_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)

[0283] wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

[0284] When the glassy alloy has the above composition, the temperaturedifference ΔT_(x) in a supercooled liquid is at least 20 K.

[0285] Preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.35 by atomic ratio, 0atomic percent<x2≦15 atomic percent, 8 atomic percent≦v2≦18 atomicpercent, 0.5 atomic percent≦z2≦7.4 atomic percent, and 3 atomicpercent≦w2≦14 atomic percent.

[0286] When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in a supercooled liquid is 40 K or more.

[0287] More preferably, the subscripts a2, b2, x2, v2, z2, and w2satisfy the relationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.28 byatomic ratio, 0 atomic percent<x2≦10 atomic percent, 11.3 atomicpercent≦v2≦14 atomic percent, 1.8 atomic percent≦z2≦4.6 atomic percent,and 5.3 atomic percent≦w2≦8.6 atomic percent.

[0288] When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in a supercooled liquid is 60 K or more.

[0289] The glassy alloy of the present invention contains Fe, Al, and atleast one element Q. That is, the glassy alloy of the present inventiondoes not contain Ga, which is contained in a conventional GeAlGaPCB(Si)alloy, but does contain an increased amount of Al. Thus, this glassyalloy has a large temperature difference ΔT_(x) in a supercooled liquidand exhibits significantly enhanced formability of the amorphous phase.

[0290] Since the glassy alloy exhibits significantly enhanced amorphousphase formability, the entire texture can be composed of a perfectamorphous phase. Thus, the permeability and the saturation magnetizationare significantly improved, resulting in superior soft magneticcharacteristics.

[0291] Moreover, the internal stress of the glassy alloy can be relievedwithout precipitation of the crystalline phase during annealing underproper conditions due to the perfect amorphous phase, resulting infurther improved soft magnetic characteristics.

[0292] Aluminum (Al) is an essential element for this glassy alloy. Atan Al content x of 20 atomic percent or less, this alloy has a perfectamorphous phase due to extremely enhanced amorphous formability of Al,and the amorphous alloy has a temperature difference ΔT_(x) of at least20 K in a supercooled liquid.

[0293] Since Al has a negative enthalpy of mixing with Fe and has anatomic radius which is larger than that of Fe, a combined use of Al withP, B, and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization, and can yield a thermally stable amorphous structure.

[0294] Moreover, Al raises the Curie temperature of the glassy alloy andimproves thermal stability of various magnetic characteristics.

[0295] The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

[0296] Iron (Fe) is essential for the glassy alloy of the presentinvention as a magnetic element. In the present invention, Fe may bepartially replaced with at least one element T selected from Co and Ni.A higher Fe content contributes to improved saturation magnetization ofthe resulting glassy alloy.

[0297] Carbon (C), phosphorus (P), silicon (Si), and boron (B) as theelement Q contribute to the formation of an amorphous phase.

[0298] When both phosphorus and silicon are added in combination, thetotal content v2 of the phosphorus and silicon is preferably more than 0to 22 atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v2 contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

[0299] The subscript b2 representing the relative Si and P contents byatomic ratio is preferably in the range of 0<b2≦0.8 when 0 atomicpercent<v2≦22 atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v2≦18atomic percent, or 0.1≦b2≦0.28 when 11.3 atomic percent≦v≦14 atomicpercent.

[0300] When the subscript b2 exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

[0301] Herein, the Si content in the glassy alloy is in the range ofpreferably 17.6 atomic percent or less, more preferably 0.8 to 6.3atomic percent, and most preferably 1.13 to 3.92 atomic percent.

[0302] The above-mentioned ranges of the subscripts b2 and v2representing the P and Si contents, respectively, contribute to anincreased temperature difference ΔT_(x) in a supercooled liquid.

[0303] The subscript z2 representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

[0304] The subscript w2 representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

[0305] The glassy alloy may contain 4 atomic percent or less Ge, and 0to 7 atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

[0306] The glassy alloy of the present invention has a temperaturedifference ΔT_(x) of at least 35 K in the above-described composition orat least 50 K in an optimized composition.

[0307] The glassy alloy of the present invention may contain otherincidental impurities.

[0308] This magnetic core can be produced by the above-described method.

[0309] The magnetic core composed of the above composition exhibitinglow core loss and permeability suppresses heat dissipation duringoperation, does not require a gap for preventing magnetic saturation,and does not generate a leakage magnetic field which adversely affectsthe other peripheral circuits.

[0310] Since the glassy alloy used has a resistivity of at least 1.5μΩ•m, the resulting magnetic powder core shows further reduced core lossdue to reduced eddy current loss in the glassy alloy particles in ahigh-frequency region. As a result, the magnetic core exhibits furtherreduced core loss and heat dissipation.

[0311] Moreover, the insulating material contributes to an increase inresistivity of the entire magnetic core. Thus, the magnetic coreexhibits further reduced core loss due to decreased eddy current loss.

[0312] The above embodiments describe the formation of the magnetic coreby discharge plasma sintering compaction molding of a mixture of aglassy alloy powder and a insulating material. The magnetic core,however, may be formed by any other process, for example, a conventionalpowder molding process, a hot pressing process, or an extruding process.

[0313] A filter in accordance with the present invention comprises acapacitor and an inductor of a coil wound around a magnetic core,wherein the magnetic core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy havinga texture primarily composed of an amorphous phase and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0314] This filter is mounted at the output side of an amplifier tosmooth an output current from the amplifier. An example of theamplifying device having this filter includes an amplifier foroutputting a pulsed current and a filter connected to the output side ofthe amplifier for smoothing the pulsed current.

[0315]FIG. 27 shows an inductor used in the filter in accordance withthe present invention, and FIG. 28 is a circuit diagram of an amplifyingdevice provided with this filter.

[0316] As shown in FIG. 27, the inductor 81 includes a magnetic core 82and a coil 83 wound therearound. As shown in FIG. 28, the amplifyingdevice 84 includes an amplifier 85 for outputting a pulsed current and afilter 86 in accordance with the present invention which is connected tooutput terminals 85 b of the amplifier 85 and smoothes the pulsedcurrent from the amplifier 85. The filter 86 consists of a capacitor 87and the inductor 81 shown in FIG. 27.

[0317] The filter 86 is a so-called low-pass filter in which thecapacitor 87 and the inductor 81 are connected to each other so as toform an L shape. Preferably, the amplifier 85 is a pulse-widthmodulation amplifier.

[0318] The operation of the amplifying device 84 will now be described.

[0319] An AC current with a voltage V1 shown in FIG. 29 is input toinput terminals 85 a of the amplifier 85. The amplifier 85 convertshigh-voltage portions of the input AC voltage into broader pulse wavesand low-voltage portions into narrower pulse waves. Moreover, theamplifier 85 amplifies the voltage and outputs the pulsed current shownin FIG. 30 through the output terminals 85 b. The filter 86 smoothesthis pulsed current and outputs the smoothed current through outputterminals 86 a of the filter 86. The output current is an amplified ACcurrent of a voltage V2 (V2>V1) as shown in FIG. 31.

[0320] As described above, a pulsed current is input to the filter 86 inaccordance with the present invention. Since the width and the voltageof the pulsed current periodically vary, a high-frequency current isapplied to the inductor 81.

[0321] In order to achieve an amplifying device with low loss andreduced waveform distortion, the loss of the inductor 81 must bereduced. Thus, the requirements for the magnetic core 82 constitutingthe inductor 81 are low core loss and substantially constant amplitudepermeability with a change in magnetic field.

[0322] The magnetic core 82 constituting the filter of the presentinvention is a molded article of a mixture of a glassy alloy powderhaving resistivity of at least 1.5 μΩ•cm and an insulating material, andthe glassy alloy powder has a texture primarily composed of an amorphousphase and has a temperature difference ΔT_(x), which is represented bythe equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooledliquid, wherein T_(x) indicates the crystallization temperature andT_(g) indicates the glass transition temperature.

[0323] The magnetic core 82 shown in FIG. 27 is toroidal. The shape ofthe magnetic core 82, however, is not limited to this. For example, themagnetic core 82 may be ellipsoidal, oval, E-shaped, U-shaped, orI-shaped in a plan view.

[0324] The magnetic core 82 is composed of a magnetic powder core inwhich glassy alloy particles are bonded to each other with an insulatingmaterial and are dispersed in the texture. Thus, the glassy alloyparticles are not dissolved into the matrix as a uniform texture. Theindividual glassy alloy particles are preferably insulated from eachother in the insulating material. Accordingly, the magnetic core 82 haslarge resistivity due to the effects of the insulating material, lowcore loss due to reduced eddy current loss, less reduction inpermeability in a high-frequency region and substantially constantamplitude permeability with a change in magnetic field.

[0325] When the temperature difference ΔT_(x) in the supercooled liquidof the glassy alloy is less than 20 K, it is difficult to adequatelyrelieve the internal stress without crystallization at an annealingtreatment after the compaction molding of the mixture of the glassyalloy powder and the insulating material. When the temperaturedifference ΔT_(x) is at least 20 K, the annealing can be performed at alower temperature which does not cause excess decomposition of theinsulating layer and increased loss.

[0326] Since the glassy alloy having a specific composition has atemperature difference ΔT_(x) of 60 K or more, the internal stress inthe magnetic core 82 can be adequately relieved during annealing. Thus,the magnetic core 82 exhibits improved soft magnetic characteristicswithout loss due to deterioration of the insulating material duringannealing at a reduced temperature. Moreover, the magnetic core 82exhibits low core loss due to relaxation of the internal stress duringthe annealing and reduces heat dissipation.

[0327] The magnetic core 82 shows a small change in permeability with achange in operational frequency and high permeability in high-frequencyranges, contributing improved frequency characteristics of the filter86.

[0328] Preferably, the rate of change in amplitude permeability of themagnetic core 82 in a magnetic field of 2,000 A/m is within ±10% of anamplitude permeability in a magnetic field of 200 A/m, and thepermeability of the magnetic core at 100 kHz is in the range of 50 to200.

[0329] Within the above rate of change, the output waveform from thefilter 86 is less distorted. Moreover, the number of turns of the coil83 can be reduced, thus resulting in a reduction in size of the inductor81. Accordingly, the sizes of the filter 86 and the amplifying device 84can be reduced. For example, the filter 86 exhibits superiorcharacteristics when the number of turns of the coil 83 is 30.

[0330] The insulating material enhances resistivity of the magnetic core82 and maintains the shape of the magnetic core 82 by binding the glassyalloy particles. Insulating materials which do not cause large loss inmagnetic properties are preferred. Examples of such insulating materialsinclude liquid or powdered organic compounds, e.g., epoxy resins,silicone resins, phenolic resins, urea resins, melamine resins, andpolyvinyl alcohol (PVA); liquid glass, i.e., Na₂O—SiO₂; oxide glasspowders, e.g., Na₂O—B₂O₃—SiO₂, PbO—B₂O₃—SiO₂, PbO—BaO—SiO₂,Na₂O—B₂O₃—ZnO, CaO—BaO—SiO₂, Al₂O₃—B₂O₃—SiO₂, and B₂O₃—SiO₂; and glassysubstances formed by sol-gel processes and primarily composed of SiO₂,Al₂O₃, ZrO₂l and TiO₂.

[0331] The insulating material may be used together with a stearate saltas a lubricant. Examples of stearate salts include zinc stearate,calcium stearate, barium stearate, magnesium stearate, and aluminumstearate.

[0332] The glassy alloy powder contains a primary phase having aresistivity of at least 1.5 μ•Ω and a temperature difference ΔT_(x) ofat least 20 K in a supercooled liquid. The glassy alloy powder isprepared by pulverizing a glassy alloy tape, by atomizing the melt ofthe glassy alloy onto a cooling roller, by atomizing the melt of theglassy alloy together with a pressurized gas into the atmosphere, or byatomizing the melt of the glassy alloy into water. The resulting glassyalloy powder exhibits low core loss and superior soft magneticcharacteristics.

[0333] The glassy alloy has a large temperature difference ΔT_(x) of 40K or more, particularly 50 K or more, and more particularly 60 k ormore, and has a large resistivity of at least 1.5 μΩ•m under optimizedcompositions. These properties are not obtainable from conventionalalloys. Moreover, the glassy alloy exhibits the superior soft magneticcharacteristics at room temperature, unlike conventional alloys.

[0334] In the supercooled region, which correspond to the temperaturedifference ΔT_(x), the glassy alloy of the present invention maintains aliquid arrangement of atoms. The mobility of these atoms is so low thatcrystallization does not substantially occur, although atomic vibrationoccurs.

[0335] In the glassy alloy having a large temperature difference ΔT_(x),the atomic mobility is low during cooling the melt, and the supercooledliquid state is maintained over a broad temperature range. Since theglassy alloy of the present invention has a large temperature differenceΔT_(x) in a supercooled liquid, the alloy is readily supercooled to atemperature below a glass transition temperature T_(g) without beingcrystallized during a cooling step of the melt, readily forming anamorphous phase.

[0336] Thus, the amorphous phase can be formed at a relatively lowcooling rate. For example, a glassy alloy powder primarily composed ofan amorphous phase is obtainable by pulverizing a bulk glassy alloy,which is prepared by a casting process, in addition to liquid quenchingprocesses having relatively high cooling rates, such as a single-rollerprocess.

[0337] The glassy alloy used in the magnetic core 82 is primarilycomposed of Fe, and contains Al and the element Q. The element Q may notinclude Si.

[0338] The glassy alloy is represented by, for example, the followingformula:

(Fe_(1-a2)T_(a2))_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)

[0339] wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0≦b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.

[0340] When the glassy alloy has the above composition, the temperaturedifference ΔT_(x) in a supercooled liquid is at least 20 K.

[0341] Preferably, the subscripts a2, b2, x2, v2, z2, and w2 satisfy therelationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.35 by atomic ratio, 0atomic percent<x2≦15 atomic percent, 8 atomic percent≦v2≦18 atomicpercent, 0.5 atomic percent≦z2≦7.4 atomic percent, and 3 atomicpercent≦w2≦14 atomic percent.

[0342] When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in the supercooled liquid is 40 K or more.

[0343] More preferably, the subscripts a2, b2, x2, v2, z2, and w2satisfy the relationships, 0≦a2≦0.15 by atomic ratio, 0.1≦b2≦0.28 byatomic ratio, 0 atomic percent<x2≦10 atomic percent, 11.3 atomicpercent≦v2≦14 atomic percent, 1.8 atomic percent≦z2≦4.6 atomic percent,and 5.3 atomic percent≦w2≦8.6 atomic percent.

[0344] When the glassy alloy has the above preferred composition, thetemperature difference ΔT_(x) in the supercooled liquid is 60 K or more.

[0345] The glassy alloy of the present invention contains Fe, Al, P, C,B, and Si. That is, the glassy alloy of the present invention does notcontain Ga, which is contained in a conventional GeAlGaPCB(Si) alloy,but does contain an increased amount of Al. Thus, this glassy alloy hasa large temperature difference ΔT_(x) in a supercooled liquid andexhibits significantly enhanced formability of the amorphous phase.

[0346] Since the glassy alloy exhibits significantly enhanced amorphousphase formability, the entire texture can be composed of a perfectamorphous phase. Thus, the permeability and the saturation magnetizationare significantly improved, resulting in superior soft magneticcharacteristics.

[0347] Aluminum (Al) is an essential element for this glassy alloy. Atan Al content x of 20 atomic percent or less, this alloy has a perfectamorphous phase due to extremely enhanced amorphous formability of Al,and the amorphous alloy has a temperature difference ΔT_(x) of at least20 K in a supercooled liquid.

[0348] Since Al has a negative enthalpy of mixing with Fe and has anatomic radius which is larger than that of Fe, a combined use of Al withP, B, and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

[0349] Moreover, Al raises the Curie temperature of the glassy alloy andimproves thermal stability of various magnetic characteristics.

[0350] The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

[0351] Iron (Fe) is essential for the glassy alloy of the presentinvention as a magnetic element. In the present invention, Fe may bepartially replaced with at least one element T selected from Co and Ni.A higher Fe content contributes to improved saturation magnetization ofthe resulting glassy alloy.

[0352] Carbon (C), phosphorus (P), silicon (Si), and boron (B) as theelement Q contribute to the formation of an amorphous phase.

[0353] When both phosphorus and silicon are added in combination, thetotal content v2 of the phosphorus and silicon is preferably more than 0to 22 atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v2 contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid.

[0354] The subscript b2 representing the relative Si and P contents byatomic ratio is preferably in the range of 0<b2≦0.8 when 0 atomicpercent<v2≦22 atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v2≦18atomic percent, or 0.1≦b2≦0.28 when 11.3 atomic percent≦v≦14 atomicpercent.

[0355] When the subscript b2 exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

[0356] Herein, the Si content in the glassy alloy is in the range ofpreferably 17.6 atomic percent or less, more preferably 0.8 to 6.3atomic percent, and most preferably 1.13 to 3.92 atomic percent.

[0357] The above-mentioned ranges of the subscripts b2 and v2representing the P and Si contents, respectively, contribute to anincreased temperature difference ΔT_(x) in a supercooled liquid.

[0358] The subscript z2 representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

[0359] The subscript w2 representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

[0360] The glassy alloy may contain 4 atomic percent or less Ge, and 0to 7 atomic percent of at least one element selected from the groupconsisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

[0361] The glassy alloy of the present invention has a temperaturedifference ΔT_(x) of at least 35 K in the above-described composition orat least 50 K in an optimized composition.

[0362] The glassy alloy of the present invention may contain otherincidental impurities.

[0363] This magnetic core can also be produced by the above-describedmethod.

[0364] The resulting magnetic core 82 containing the glassy alloyexhibits superior soft magnetic characteristics at room temperature andthe soft magnetic characteristics are further improved by annealing.This magnetic core 82 exhibits reduced core loss compared to that ofconventional materials and substantially constant permeability with achange in magnetic field, and is preferably used in the filter 86 whichrequires superior soft magnetic characteristics.

[0365] In addition to the above-described compaction molding in thedischarge plasma sintering apparatus, the magnetic core 82 may be formedby other compaction molding processes, such as conventional powdermolding, hot pressing, and extruding.

[0366] The filter 86 includes the magnetic core 82, which is formed of amixture of the above-mentioned glassy alloy powder and theabove-mentioned insulating material. The insulating material contributesto increased resistivity of the entire magnetic powder core and reducedcore loss due to decreased eddy current loss in the magnetic core 82.The resulting filter 86 exhibits low loss and less heat dissipation.Moreover, the magnetic core 82 composed of the glassy alloy powderexhibits a small reduction in permeability in a high-frequency region,thus resulting in improved frequency characteristics of the filter 86.

[0367] Since the magnetic core 82 contains the glassy alloy having aresistivity of at least 1.5 μΩ•m, the resulting magnetic core showsfurther reduced core loss due to reduced eddy current loss in the glassyalloy particles in a high-frequency region. The resulting filter 86exhibits low loss and less heat dissipation.

[0368] Since the rate of change in amplitude permeability of themagnetic core 82 in a magnetic field of 2,000 A/m is within ±10% of anamplitude permeability in a magnetic field of 200 A/m, the pulsed ACcurrent can be smoothed without waveform distortion, the filter 86outputting waveforms with less distortion.

[0369] Moreover, the magnetic core 82 has a permeability of the magneticcore in the range of 50 to 200 at 100 kHz. Thus, the size of theinductor 81 can be reduced by decreasing the number of turns of the coil83, thus reduction in size of the filter 86 or the amplifying device 84.

[0370] The amplifying device 84 including the filter 86 with low lossand reduced waveform distortion exhibits reduced heat dissipation andoutputs a current with reduced distortion.

[0371] The composition of the glassy alloy in accordance with thepresent invention will now be described in more detail.

[0372] The amorphous soft-magnetic alloy of the present inventioncomprises Fe, Al, P, C, Si, and B and has a texture primarily composedof an amorphous phase. In addition, this amorphous alloy has atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.

[0373] Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic component and Al, P, C, Si, and B havingamorphous formability, the amorphous alloy exhibits superior softmagnetic characteristics.

[0374] In particular, an amorphous soft-magnetic alloy exhibiting atemperature difference ΔT_(x) of at least 20 K in a supercooled liquidis called a glassy alloy. The glassy alloy can has a temperaturedifference ΔT_(x) of at least 40 K and particularly at least 60 K in anoptimized composition, which is not anticipated from conventionalknowledge. The glassy alloy also exhibits superior soft magneticcharacteristics at room temperature.

[0375] The amorphous soft-magnetic alloy primarily composed of anamorphous phase has small coercive force and thus exhibits superior softmagnetic characteristics.

[0376] Since the amorphous soft-magnetic alloy of the present inventionhas a large temperature difference ΔT_(x) in a supercooled liquid, thealloy is readily supercooled to a temperature below a glass transitiontemperature T_(g) without being crystallized during a cooling step ofthe melt, readily forming an amorphous phase. Thus, the amorphous phasecan be formed at a relatively low cooling rate. For example, a glassyalloy powder primarily composed of an amorphous phase is obtainable bypulverizing a bulk glassy alloy, which is prepared by a casting orinjection process, in addition to liquid quenching processes havingrelatively high cooling rates, such as a single-roller process.

[0377] Moreover, the amorphous soft-magnetic alloy of the presentinvention exhibits a high Curie temperature and superior thermalstability.

[0378] The glassy alloy may be represented by the following formula:

(Fe_(1-a)T_(a))_(100-x-v-z-w)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w)

[0379] wherein T represents at least one element of Co and Ni, and thesubscripts a, b, x, v, z, and w satisfy the relationships, 0≦a≦0.15 byatomic ratio, 0≦b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomicpercent, 0 atomic percent<v≦22 atomic percent, 0 atomic percent<z≦12atomic percent, and 0 atomic percent<w≦16 atomic percent. This amorphoussoft-magnetic alloy has a temperature difference ΔT_(x) of at least 20 Kin a supercooled liquid.

[0380] Preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.35 byatomic ratio, 0 atomic percent<x≦15 atomic percent, 8 atomicpercent<v≦18 atomic percent, 0.5 atomic percent≦z≦7.4 atomic percent,and 3 atomic percent≦w≦14 atomic percent. This amorphous soft-magneticalloy has a temperature difference ΔT_(x) of at least 40 K in asupercooled liquid.

[0381] More preferably, the subscripts a, b, x, v, z, and w satisfy therelationships, 0≦a≦0.15 by atomic ratio, 0.1 by atomic ratio≦b≦0.28 byatomic ratio, 0 atomic percent<x≦10 atomic percent, 11.3 atomicpercent<v≦14 atomic percent, 1.8 atomic percent≦z≦4.6 atomic percent,and 5.3 atomic percent≦w≦8.6 atomic percent. This amorphoussoft-magnetic alloy has a temperature difference ΔT_(x) of at least 60 Kin a supercooled liquid.

[0382] Fe—Al—Ga—C—P—Si—B glassy alloys are known. This glassy alloycontains iron (Fe) and other elements which facilitate the formation ofan amorphous phase, such as aluminum (Al), gallium (Ga), carbon (C),phosphorus (P), silicon (Si), and boron (B).

[0383] On the other hand, the glassy alloy of the present inventioncontains Fe, Al, C, P, Si, and B. That is, the glassy alloy of thepresent invention does not contain Ga, but does contain an increasedamount of Al. Thus, it is confirmed that the glassy alloy of the presentinvention can contain an amorphous phase regardless of the omission ofGa, which has been considered to be an essential element for theformation of the amorphous layer, and that this glassy alloy has a largetemperature difference ΔT_(x) in a supercooled liquid.

[0384] The amorphous soft-magnetic alloy of the present inventionexhibits high amorphous formability compared to the conventionalFe—Al—Ga—C—P—Si—B alloy. Since a perfect amorphous phase can be formedat a decreased cooling rate, a bulk alloy having a relatively large sizeand containing an amorphous phase can be produced by a casting process.

[0385] Since the entire texture is composed of a complete amorphousphase, the amorphous soft-magnetic alloy of the present inventionexhibits significantly improved permeability and saturationmagnetization compared to conventional glassy alloys, resulting insuperior soft magnetic characteristics.

[0386] The internal stress in the amorphous soft-magnetic alloy can berelieved under an appropriate condition without precipitation of acrystalline phase, and the soft magnetic characteristics are furtherimproved.

[0387] Aluminum (Al) is an essential element for the amorphoussoft-magnetic alloy of the present invention. At an Al content x of 20atomic percent or less, this alloy has a perfect amorphous phase due toextremely enhanced amorphous formability of Al, and the amorphoussoft-magnetic alloy has a temperature difference ΔT_(x) of 20 K or morein a supercooled liquid.

[0388] Since Al has a negative enthalpy of mixing with Fe and has anatomic radius which is larger than that of Fe, a combined use of Al withP, B, and Si, which have atomic radii smaller than that of Fe, inhibitscrystallization and can yield a thermally stable amorphous structure.

[0389] Moreover, Al raises the Curie temperature of the amorphoussoft-magnetic alloy and improves thermal stability of various magneticcharacteristics.

[0390] The Al content x2 is preferably 20 atomic percent or less, morepreferably more than 0 atomic percent to 15 atomic percent, and mostpreferably more than 0 atomic percent to 10 atomic percent. An Alcontent x2 exceeding 20 atomic percent, the alloy has a decreasedsaturation magnetization due to a relatively low Fe content and does nothave a temperature difference ΔT_(x) in a supercooled liquid.

[0391] Iron (Fe) is essential for the amorphous soft-magnetic alloy ofthe present invention as a magnetic element. The iron (Fe) may bepartially replaced with at least one element T selected from Co and Ni.A higher Fe content contributes to improved saturation magnetization ofthe resulting amorphous soft-magnetic alloy.

[0392] Carbon (C), phosphorus (P), silicon (Si), and boron (B areelements having amorphous formability. A multicomponent compositionincluding these elements, in addition to Fe and Al, facilitates theformation of a stable amorphous phase, compared to an Fe—Al binarycomposition.

[0393] In particular, phosphorus (P) having high amorphous formabilityfacilitates the formation of an amorphous phase over the entire textureand the occurrence in a temperature difference ΔT_(x) in a supercooledliquid.

[0394] Combined use of P and Si further increases the temperaturedifference ΔT_(x) in the supercooled liquid and facilitates theformation of a large bulk alloy composed of a single amorphous phase.

[0395] When both phosphorus and silicon are added in combination, thetotal content v of the phosphorus and silicon is preferably more than 0to 22 atomic percent, more preferably 8 to 18 atomic percent, and mostpreferably 11.3 to 14 atomic percent. The combined use of P and S with apreferred total content v contributes to an improved temperaturedifference ΔT_(x) in a supercooled liquid and an increased size in abulk alloy composed of a single amorphous phase.

[0396] The subscript b representing the relative Si and P contents byatomic ratio is preferably in the range of 0<b≦0.8 when 0 atomicpercent<v≦22 atomic percent, 0.1≦b≦0.35 when 8 atomic percent≦v≦18atomic percent, or 0.1≦b≦0.28 when 11.3 atomic percent≦v≦14 atomicpercent.

[0397] When the subscript b exceeds 0.8, an excess amount of Si mayundesirably cause disappearance of the temperature difference ΔT_(x) inthe supercooled liquid.

[0398] Herein, the Si content in the amorphous soft-magnetic alloy is inthe range of preferably 17.6 atomic percent or less, more preferably 0.8to 6.3 atomic percent, and most preferably 1.13 to 3.92 atomic percent.

[0399] The above-mentioned ranges for the subscripts b and vrepresenting the P and Si contents, respectively, contribute to anincreased temperature difference ΔT_(x) in a supercooled liquid and anincrease in size of a bulk alloy having a single amorphous phase.

[0400] The subscript z representing the C content is in the range ofpreferably more than 0 to 12 atomic percent, more preferably 0.5 to 7.4atomic percent, and most preferably 1.8 to 4.6 atomic percent.

[0401] The subscript w representing the B content is in the range ofpreferably more than 0 to 16 atomic percent, more preferably 3 to 14atomic percent, and most preferably 5.3 to 8.6 atomic percent.

[0402] The amorphous soft-magnetic alloy may contain 4 atomic percent orless Ge, and 0 to 7 atomic percent of at least one element selected fromthe group consisting of Nb, Mo, Hf, Ta, W, Zr, and Cr.

[0403] The amorphous soft-magnetic alloy of the present invention has atemperature difference ΔT_(x) of at least 35 K in the above compositionor at least 50 K in an optimized composition.

[0404] The amorphous soft-magnetic alloy of the present invention maycontain other incidental impurities.

[0405] The amorphous soft-magnetic alloy of the present invention may beformed by a casting process, a single- or twin-roller quenching process,a spinning-in-liquid process, an atomizing process in high-pressure gas,or a casting process of a melt into various shapes, e.g., a bulk, atape, a wire, or a powder. In particular, an amorphous soft-magneticalloy having a thickness and a diameter which are ten or more timesthose of conventional amorphous soft-magnetic alloys can be formed by asingle-roller quenching process, a casting process, or an injectionprocess.

[0406] The resulting amorphous soft-magnetic alloy exhibits magnetism atroom temperature and improved magnetism after annealing. This amorphoussoft-magnetic alloy is applicable to various magnetic articles.

[0407] The preferred cooling rate depends on the composition of thealloy, the type of the cooling process, and the size and shape of thearticle, and is generally in the range of 1 to 10 K/s. The cooling rateis determined so that the glass phase does not contain precipitatedcrystalline phases, such as Fe₃B, Fe₂B, and Fe₃P phases.

[0408] As an exemplary process for making the amorphous soft-magneticalloy, an injection process using an injection mold will now bedescribed. In this injection process, a melt of an amorphoussoft-magnetic alloy having the above composition is injected into atoroidal cavity of a mold through a nozzle so that the melt is cooledand solidified in the cavity to form a toroidal article. The melt isinjected into the mold along a tangent line of the outer mold surface.

[0409]FIGS. 32, 33A and 33B show an injection mold. This mold 121includes a hollow cylinder 141 formed of a rolled sheet 140, an uppermold 125, and a lower mold 126. The upper mold 125 comes into contactwith a parting plane 129, while protuberances 127 of the upper mold 125engages with recesses 128 of the lower mold 126 so that the relativeposition between the upper mold 125 and the lower mold 126 is securedand the hollow cylinder 141 is inserted into a hole 120 passing throughthe upper mold 125.

[0410] The parting plane 129 of the lower mold 126 is provided with ashallow circular recess 122 in the substantial center thereof. Theparting plane 129 is provided with a sprue 123 and a gate 124 thereon.The sprue 123 communicates with the recess 122 and extends along atangent line of the peripheral wall 122 a of the recess 122, the tangentline being parallel to the recesses 128 of the lower mold 126. Therecess 122 and the sprue 123 have substantially the same depth. The gate124 communicates with a side wall of the lower mold 126.

[0411] The hollow cylinder 141 is inserted into the hole 120 so that thebottom end 141 a of the hollow cylinder 141 comes into contact with thesurface 122 b of the recess 122. The peripheral face 141 b of the hollowcylinder 141 and the peripheral wall 122 a of the recess 122 are therebyconcentrically arranged so as to form a toroidal cavity A, as shown inFIG. 33A. Thus, the peripheral wall 122 a of the recess 122 defines theouter diameter of the cavity A, whereas the peripheral face 141 b of thehollow cylinder 141 defines the inner diameter of the cavity A.

[0412] As shown in FIG. 32, the hollow cylinder 141 is formed by rollinga rectangular sheet 140 so that both ends 142 and 143 thereof overlap.The rolled sheet 140 is inserted into the hole 120 in the upper mold 125and is supported as the hollow cylinder 141 by the inner wall 120 a ofthe hole 120. Since, these ends 142 and 143 are not affixed to eachother, the diameter of the hollow cylinder 141 is appropriatelychangeable. Thus, the inner diameter of the cavity A is also changeable.

[0413] The rectangular sheet 140 may be formed of any material which isnot reactive with the melt of the amorphous soft-magnetic alloy, has amelting point above the temperature (1,000 to 1,400° C.) of the melt,and exhibits high thermal conductivity. Examples of such materialsinclude metal foils of copper (Cu), aluminum (Al), gold (Au), silver(Ag), and platinum (Pt), and carbon sheets. A copper foil is preferred.

[0414] It is preferable that the thermal expansion coefficient of thehollow cylinder 141 be the same as that of the amorphous soft-magneticalloy, since the hollow cylinder 141 similarly expands or shrinks by theheat of melt of the amorphous soft-magnetic alloy injected into themold.

[0415] As shown in FIG. 33A, the peripheral wall 122 a of the cavity Ais partly cut out and communicates with the sprue 123. One side wall ofthe sprue 123 extends along a tangent line of the peripheral wall 122 aof the recess 122, the tangent line being parallel to the recesses 128.

[0416] The peripheral wall 122 a is also connected to the other sidewall of the sprue 123. The other side wall extends along a tangent lineof the peripheral face 141 b of the hollow cylinder 141. These two sidewalls of the sprue 123 are parallel to each other.

[0417] It is preferable that the sprue 123 extends along the tangentline of the peripheral wall 122 a of the cavity A. In the presentinvention, the sprue 123 may slightly shift from the tangent line aslong as the sprue 123 communicates with the cavity A.

[0418] In injection molding using the mold 121, as shown in FIGS. 32 and33A, the upper mold 125 is engaged with the lower mold 126 and thehollow cylinder 141 is inserted into the hole 120 of the upper mold 125to form the cavity A. A nozzle 131 for supplying a melt for an amorphoussoft-magnetic alloy is put into contact with the gate 124. The melt isejected from the nozzle 131 by pressure of an inert gas which issupplied from a gas supply source not shown in the drawings. The ejectedmelt enters the cavity A through the gate 124 and the sprue 123.

[0419] Since the sprue 123 extends along the tangent line of theperipheral wall 122 a of the cavity A in a direction parallel to therecesses 128, the ejected melt enters the cavity A along the peripheralwall 122 a in the Z direction in FIG. 33A without diversion.

[0420] The melt is cooled in the sprue 123 and the cavity A and issolidified in the cavity A to form a ring. The diameter of the hollowcylinder 141 is r₁ before the injection of the melt into the cavity A asshown in FIG. 33A, and decreases to r₂ by the deformation of the hollowcylinder 141 due to a reduction in volume during solidification of themelt. An injection-molding precursor 151 primarily composed of anamorphous phase is formed in such a manner, as shown in FIG. 34.

[0421] The injection-molding precursor 151 consists of a ring portion152 and a sprue portion 153. The sprue portion 153 is removed to form aring injection-molding article 111 of the amorphous soft-magnetic alloy.

[0422] In order to prevent clogging in the nozzle 131 due to oxidationof the melt, the injection of the melt into the mold 121 is preferablyperformed in a low-oxygen atmosphere, such as an inert gas or vacuumatmosphere.

[0423] The temperature of the melt is in the range of preferably(T_(m)−100) K to (T_(m)+300) K and more preferably T_(m) K to(T_(m)+100) K, wherein T_(m) indicates the melting point of theamorphous soft-magnetic alloy. At a temperature of less than (T_(m)−100)K, clogging and crystallization of the melt may in the nozzle 131 occurdue to an unstable supercooled state. At a temperature exceeding(T_(m)+300) K, no particular effects reflecting this temperature arefound.

[0424] For example, an amorphous soft-magnetic alloy having acomposition of Fe₇₀Al₇P_(9.65)C_(3.45)B_(6.9)Si₃ has a melting point of1,317 K. Thus, the temperature of this melt is preferably in the rangeof 1,217 to 1,617 K and more preferably 1,317 to 1,417 K.

[0425] The injection pressure of the melt is in the range of preferably29 to 490 kPa and more preferably 98 to 294 kPa. At an injectionpressure of less than 29 kPa, the entire cavity is not filled with themelt. At an injection pressure exceeding 490 kPa, the melt may leak fromthe junction between the upper mold 125 and the lower mold 126 of themold 121, and stress may remain in the molded article.

[0426] Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic component and Al, P, C, Si, and B havingamorphous formability, the amorphous alloy exhibits superior softmagnetic characteristics. Since Al has high amorphous formability, theentire texture is amorphous.

[0427] Since this amorphous soft-magnetic alloy has a large temperaturedifference ΔT_(x) of at least 20 K in a supercooled liquid, an amorphousphase can be formed from a melt at a relatively low cooling rate. Thus,a bulk alloy which is thicker than a tape can be produced. Inparticular, a bulk cast or injection molding article can be formed by acasting or injection process using a melt of an alloy. The abovedescribed switching power supply, filter, and amplifying device usingthis molded article exhibits superior characteristics.

[0428] This amorphous soft-magnetic alloy exhibits high amorphousformability compared to the conventional Fe—Al—Ga—C—P—Si—B alloy. Sincea perfect amorphous phase can be formed at a decreased cooling rate, abulk alloy having a relatively large size and containing an amorphousphase can be produced by a casting process. This homogeneous bulk alloymay be pulverized in order to produce magnetic powder cores.

[0429] Since the entire texture is composed of a complete amorphousphase, the amorphous soft-magnetic alloy exhibits significantly improvedpermeability and saturation magnetization, resulting in superior softmagnetic characteristics.

[0430] The internal stress in the amorphous soft-magnetic alloy can berelieved under an appropriate condition without precipitation of acrystalline phase due to the complete amorphous phase, and the softmagnetic characteristics are further improved.

EXAMPLES Example 1 Properties of Magnetic Powder Core Composed of GlassyAlloy Prepared by Single-Roller Process

[0431] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃. This ingot was melted in a crucibleand was jetted onto a rotating roller through a nozzle in areduced-pressure Ar atmosphere by a single-roller process to quench themelt and to form a glassy alloy tape with a width of 15 mm and athickness of 20 μm of an amorphous texture. The tape was pulverized inair using a rotor mill and the trituration was classified to selectparticles with diameters of 45 to 150 μm as a glassy alloy powder.

[0432] A mixture of 97 parts by weight of glassy alloy powder, 1 part byweight of calcium stearate as an insulating material, and 2 parts byweight of liquid glass was dried at 473 K (200° C.) for 1 hour in airand was disintegrated. The mixture was loaded into a tungsten carbidemold shown in FIG. 2 and was heated from room temperature (298 K or 25°C.) to a molding temperature T_(s) of 573 K (300° C.) or 623 K (350° C.)by a pulsed current from an energizing unit under a pressure P_(s) of600 MPa or 900 MPa using the upper and lower punches 12 and 13,respectively, in the discharge plasma sintering apparatus of a reducedpressure atmosphere of 6.6×10³¹ ³ Pa. The mixture was held at themolding temperature T_(s) for approximately 8 minutes while maintainingthe above molding pressure P_(s) to complete the compression molding.

[0433] The molded article was annealed at an annealing temperature T_(a)of 573 (300° C.) to 723 K (450° C.) for 3,600 seconds to produce arequired number of toroidal magnetic powder cores with an outer diameterof 12 mm, an inner diameter of 6 mm, and a thickness of 2 mm.

Properties of Glassy Alloy Powder

[0434]FIG. 4 shows the X-ray diffraction patterns of the powder and thetape of the glassy alloy having the compositionFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃. As shown in FIG. 4, both the powderand the tape have broad X-ray diffraction patterns which are inherent inamorphous textures. The amorphous phase is maintained afterpulverization of the glassy alloy tape.

[0435]FIG. 5 shows differential scanning calorimetric (DSC) thermogramsof the powder and the tape of the above glassy alloy at a heating rateof 40 K/min (=0.67 K/sec). According to these DSC thermograms, theglassy alloy tape has a glass transition temperature T_(g) at 760 K anda crystallization temperature T_(x) at 821 K, thus the temperaturedifference ΔT_(x) (=T_(x)−T_(g)) in the supercooled liquid being 61 K.The glassy alloy powder has a glass transition temperature T_(g) at 760K and a crystallization temperature T_(x) at 822 K, thus the temperaturedifference ΔT_(x) being 62 K.

[0436] Accordingly, the glassy alloy powder and tape ofFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ has a broad supercooled-liquid regionbelow the crystallization temperature T_(x), exhibits a largetemperature difference ΔT_(x), and thus has high amorphous formabilityand thermal stability.

Dependence of Magnetic Characteristics on Annealing Temperature (Ta)

[0437]FIGS. 6 and 7 show the dependence of magnetic flux density(B_(2.4k)) and the coercive force (H_(c)) on the annealing temperature(T_(a)) of the magnetic powder cores which are composed of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder and the insulatingmaterial. In FIGS. 6 and 7, the plot (▪) illustrates the results at amolding temperature T_(s) of 573 K (300° C.) and a molding pressureP_(s) of 900 MPa, the plot () illustrates the results at a moldingtemperature T_(s) of 623 K (350° C.) and a molding pressure P_(s) of 600MPa, and the plot (▴) illustrates the results at a molding temperatureT_(s) of 623 K (350° C.) and a molding pressure P_(s) of 900 MPa. In allthe cases, the holding time at the annealing temperature T_(a) was 3,600seconds. The magnetic flux density (B_(2.4k)) in FIG. 6 represents thedensity when a magnetic field of 2.4 kA/m is applied.

[0438] Magnetic powder cores for comparison were prepared as in EXAMPLE1, except that carbonyl iron powder was used instead of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder.

[0439]FIGS. 8 and 9 show the dependence of magnetic flux density(B_(2.4k)) and the coercive force (H_(c)) on the annealing temperature(T_(a)) of the magnetic powder cores which are composed of the Fe powderand the insulating material. In FIGS. 8 and 9, the plot (▪) illustratesthe results at a molding temperature T_(s) of 673 K (400° C.) and amolding pressure P_(s) of 600 MPa, the plot () illustrates the resultsat a molding temperature T_(s) of 623 K (350° C.) and a molding pressureP_(s) of 600 MPa, the plot (▴) illustrates the results at a moldingtemperature T_(s) of 573 K (300° C.) and a molding pressure P_(s) of 900MPa, and the plot (♦) illustrates the results at a molding temperatureT_(s) of 573 K (300° C.) and a molding pressure P_(s) of 600 MPa. In allthe cases, the holding time at the annealing temperature T_(a) was 3,600seconds. The magnetic flux density (B_(2.4k)) in FIG. 8 represents thedensity when a magnetic field of 2.4 kA/m is applied.

[0440]FIG. 6 illustrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits an increased magnetic flux density (B_(2.4k)) afterannealing regardless of the molding conditions, such as the moldingtemperature T_(s) and the molding pressure P_(s). The magnetic fluxdensity (B_(2.4k)) of the annealed magnetic powder core significantlyincreases at an annealing temperature T_(a) above 623 K (350° C.). Onthe other hand, the magnetic flux density (B_(2.4k)) does notsubstantially vary up to an annealing temperature T_(a) of 623 K (350°C.) under the conditions of T_(s)=673 K (400° C.) and P_(s)=600 MPa.

[0441]FIG. 7 demonstrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits a decreased coercive force (Hc) after annealingregardless of the molding conditions. The coercive force (Hc) is 100 A/mor less by annealing at an annealing temperature T_(a) in the range ofapproximately 603 K to 713 K, 80 A/m or less at an annealing temperatureT_(a) in the range of approximately 623 K to 703 K, 40 A/m or less at anannealing temperature T_(a) in the range of approximately 653 K to 703K, and is the minimum of approximately 15 A/m at 693 K (420° C.) andaround.

[0442] In contrast, as shown in FIG. 8, the magnetic flux density(B_(2.4k)) of the magnetic powder core for comparison does notsubstantially vary by annealing regardless of the molding conditionsincluding the molding temperature T_(s) and the molding pressure P_(s).

[0443] As shown in FIG. 9, the coercive force (Hc) of this magneticpowder core for comparison does also not substantially vary by annealingregardless of the molding conditions.

Frequency (f) Characteristics of Permeability and Core Loss

[0444]FIG. 10 shows the frequency (f) characteristics of thepermeability (μ′) of the magnetic powder cores which are composed of theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder and the insulatingmaterial. FIG. 11 shows the frequency (f) characteristics of the coreloss (W) of these magnetic powder cores in which the core loss wasmeasured at a frequency in the range of 10 kHz to 100 kHz and a magneticflux density (Bm) of 0.1 T. In FIGS. 10 and 11, the plot () illustratesthe results at a molding temperature T_(s) of 623 K (350° C.), a moldingpressure P_(s) of 600 MPa, and an annealing temperature T_(a) of 693 K(420° C.), and the plot (▴) illustrates the results at a moldingtemperature T_(s) of 623 K (350° C.), a molding pressure P_(s) of 900MPa, and an annealing temperature T_(a) of 683 K (410° C.). In all thecases, the holding time at the annealing temperature T_(a) was 3,600seconds.

[0445]FIGS. 12 and 13 show the frequency (f) characteristics of thepermeability (μ′) and the core loss (W) of magnetic powder cores whichwere prepared using a carbonyl iron powder and an insulating materialfor comparison in which the core loss was measured at a frequency in therange of 10 kHz to 100 kHz and a magnetic flux density (Bm) of 0.1 T. InFIGS. 12 and 13, the plot (▪) illustrates the results at a moldingtemperature T_(s) of 673 K (400° C.), a molding pressure P_(s) of 600MPa, and an annealing temperature T_(a) of 673 K (400° C.), the plot ()illustrates the results at a molding temperature T_(s) of 623 K (350°C.), a molding pressure PS of 600 MPa, and an annealing temperatureT_(a) of 673 K (400° C.), the plot (▴) illustrates the results at amolding temperature T_(s) of 573 K (300° C.), a molding pressure P_(s)of 900 MPa, and an annealing temperature T_(a) of 673 K (400° C.), andthe plot (♦) illustrates the results at a molding temperature T_(s) of573 K (300° C.), a molding pressure P_(s) of 600 MPa, and an annealingtemperature T_(a) of 673 K (400° C.). In all the cases, the holding timeat the annealing temperature T_(a) was 3,600 seconds.

[0446]FIG. 10 illustrates that the magnetic powder core using theFe₇₀Al₇P_(9.65)C2.₃B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibits a constant permeability (μ′) over a broad frequencyrange and a relatively small decrease in the permeability (μ′) in ahigh-frequency region above 1,000 kHz. Thus, this magnetic powder coreexhibits superior frequency (f) characteristics on the permeability (μ′)regardless of the molding conditions, such as the molding temperatureT_(s) and the molding pressure Ps. The magnetic powder core  (T_(s)=623K, P_(s)=600 MPa, and T_(a)=693 K) exhibits a constant permeability overthe broad frequency range of 0.3 to 10,000 kHz, and the magnetic powdercore ▴ (T_(s)=623 K, P_(s)=900 MPa, and T_(a)=683 K) exhibits a constantpermeability over the broad frequency range of 0.3 to 1,000 kHz. Thus,these magnetic powder cores are preferably applicable to magnetic corecomponents requiring a constant permeability up to a high frequencyregion, such as transformer cores for switching power supplies andsmoothing choke cores.

[0447] In contrast, as shown in FIG. 12, the magnetic powder cores forcomparison have a narrower constant permeability region compared to themagnetic powder cores of EXAMPLE 1. In the magnetic powder core ▪(T_(s)=673 K, P_(s)=600 MPa, and T_(a)=673 K), the permeabilitysignificantly decreases as the frequency increases. In the magneticpowder core  (T_(s)=623 K, P_(s)=600 MPa, and T_(a)=673 K), thepermeability significantly decreases at a frequency above 10 kHz. In themagnetic powder cores ▴ (T_(s)=573 K, P_(s)=900 MPa, and T_(a)=673 K)and ♦ (T_(s)=573 K, P_(s)=600 MPa, and T_(a)=673 K), the permeabilitysignificantly decreases at a frequency region above 200 kHz. Thesemagnetic powder cores exhibit permeabilities which are lower than thoseof the magnetic powder cores of EXAMPLE 1 in a high-frequency region of1,000 kHz or more.

[0448]FIGS. 11 and 13 show that the magnetic powder cores using theFe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ glassy alloy powder of the presentinvention exhibit lower core loss compared to the magnetic powder coresin the frequency region of 10 kHz to 100 kHz. The core loss of themagnetic powder cores of the present invention is one order of magnitudesmaller than the core loss of the magnetic powder cores for comparisonin the frequency region of 10 kHz to 20 kHz. Accordingly, the magneticpowder core of the present invention exhibits low core loss from alow-frequency region to a high-frequency region.

Dependence of Physical Properties on C, P, Si, and B Contents in GlassyAlloy

[0449] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare ingots represented the formulaFe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w). Each ingot was melted in acrucible and was jetted onto a rotating roller through a nozzle in areduced-pressure Ar atmosphere by a single-roller process to quench themelt and to form a glassy alloy tape with a width of 1 mm and athickness of 20 μm of an amorphous texture. The resulting glassy alloyshad the following compositions:

[0450] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(5.75)B_(4.6),

[0451] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(8.05)B_(4.6),

[0452] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(5.75)B_(6.9),

[0453] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9),

[0454] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(3.45)B_(4.6),

[0455] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(5.75)B_(2.3),

[0456] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(8.05)B_(2.3),

[0457] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(3.45)B_(9.2),

[0458] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(1.15)B_(9.2),

[0459] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(1.15)B_(6.9),

[0460] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(4.6)B_(5.75),

[0461] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(4.6)B_(6.9),

[0462] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(3.45)B_(8.05), and

[0463] Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(2.3)B_(8.05),

[0464] Each glassy alloy tape was subjected to DSC at a heating rate of0.67 K/sec to determine the glass transition temperature T_(g)l thecrystallization temperature T_(x), and thus the temperature differenceΔT_(x) in the supercooled liquid.

[0465]FIGS. 14, 15, and 16 show the dependence of the glass transitiontemperature T_(g), the crystallization temperature T_(x), and thetemperature difference ΔT_(x) in the supercooled liquid, respectively,on the composition of the glassy alloy.

[0466] Numbers near the corresponding plots in the ternary diagramsshown in FIGS. 14, 15, and 16 indicate the glass transition temperatureT_(g), the crystallization temperature T_(x), and the temperaturedifference ΔT_(x) in the supercooled liquid, respectively. Numbers onisothermal lines in FIGS. 14 to 16 indicate the temperatures of theisothermal lines.

[0467]FIG. 14 shows that the glass transition temperature T_(g)increases with an increased B content or a decreased C content. Theisothermal line at T=760 K lies in the range of a B content w of 4.1 to8.05 atomic percent and a C content z of 2.3 to 5.1 atomic percent.

[0468]FIG. 15 shows that the crystallization temperature T_(x) alsoincreases with an increased B content or a decreased C content. Theisothermal line at T_(x)=815 K lies in the range of a B content w of 4to 8.4 atomic percent and a C content z of 0.3 to 5 atomic percent.

[0469]FIG. 16 shows that the region surrounded by the isothermal line atT_(g)=760 K shown in FIG. 14 and the isothermal line at T_(x)=815 Kshown in FIG. 15 corresponds to the region surrounded by the isothermalline at ΔT_(x)=60 K. The temperature difference ΔT_(x) in thesupercooled liquid exceeds 60 K within this range. In particular, thetemperature difference ΔT_(x) of theFe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9) glassy alloy is 63 K.

Example 2 Properties of Magnetic Powder Core Composed of Glassy AlloyPrepared by Gas Atomizing Process

[0470] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₇A₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87). This ingot was melted in acrucible provided with an atomizing nozzle at 1,350° C. (which was atleast 140° C. higher than the melting point of the glassy alloy). Themelt was atomized together with gaseous argon with a pressure of 8.6 MPathrough the atomizing nozzle to prepare an alloy powder. The alloypowder was classified into several powders having various particle sizeranges.

[0471] A mixture of 97 parts by weight of each glassy alloy powder, 1parts by weight of calcium stearate as an insulating material, and 2parts by weight of liquid glass was prepared. The mixture was dried inan atmosphere at 473 K (200° C.) for 1 hour and was disintegrated. Themixture was loaded into a tungsten carbide mold shown in FIG. 2 and washeated from room temperature (298 K or 25° C.) to a molding temperatureT_(s) of 623 K (350° C.) by a pulsed current from an energizing unitunder a pressure P_(s) of 1,000 MPa using the upper and lower punches 12and 13, respectively, in the discharge plasma sintering apparatus of areduced pressure atmosphere of 6.6×10⁻³ Pa. The mixture was held at themolding temperature T_(s) for approximately 8 minutes while maintainingthe above molding pressure P_(s) to complete the compression molding.

[0472] The molded article was annealed at an annealing temperature T_(a)of 683 (410° C.) for 3,600 seconds to produce a required number oftoroidal magnetic powder cores with an outer diameter of 12 mm, an innerdiameter of 6 mm, and a thickness of 2 mm.

Permeability and DC Superposition Characteristic of Magnetic Powder Core

[0473] The permeability and the DC superposition characteristics ofmagnetic powders cores were measured. In each magnetic powder core, theamorphous volume fraction Vamo in the texture was 93% or 98% and theparticle size was 38 μm or less. The amorphous volume fraction Vamo wasdetermined by DSC.

[0474]FIGS. 17A and 17B show the dependence of the effectivepermeability (μ′) and the rate (Δμ′) of change in permeability,respectively, of these magnetic powder cores on the magnetic field. Inthese drawings, the plot () indicates an amorphous volume fraction of93%, and the plot (▴) indicates an amorphous volume fraction of 98%.FIG. 17B also shows the rate (Δμ′) of change in permeability of amagnetic powder core using carbonyl iron powder (COMPARATIVE EXAMPLE).

[0475]FIGS. 17A and 17B illustrate that the permeability and the rate ofchange in permeability of the magnetic powder cores according to thepresent invention do not substantially depend on the magnetic field.Thus, the magnetic powder cores of the present invention exhibit stablesoft magnetic characteristics. Moreover, the soft magneticcharacteristics are not affected by the amorphous volume fraction.

[0476] Thus, these magnetic powder cores are preferably applicable tomagnetic core components requiring a constant permeability, such astransformer cores for switching power supplies and smoothing chokecores.

[0477] In contrast, in the magnetic powder core of COMPARATIVE EXAMPLE,the rate (Δμ′) of change in permeability increases as the magnetic fieldincreases. Since this magnetic powder core exhibits large variations insoft magnetic characteristics, magnetic components, such astransformers, using this magnetic powder core will exhibit inferiorcharacteristics.

[0478]FIGS. 18A and 18B illustrate the dependence of the inductance (L)and the rate of change therein (ΔL) (so-called DC superpositioncharacteristic), respectively, on the DC bias magnetic field (H_(dc)) ofeach magnetic powder core. In these drawings, the plot () indicates anamorphous volume fraction of 93%, and the plot (▴) indicates anamorphous volume fraction of 98%. FIG. 18B also shows the rate (ΔL) ofchange in inductance of a magnetic powder core using an FeAlSi amorphousalloy powder (COMPARATIVE EXAMPLE).

[0479]FIGS. 18A and 18B illustrate that the inductance (L) and the rate(ΔL) of change in inductance of the magnetic powder cores according tothe present invention show small changes when the DC bias magnetic fieldis varied. Thus, the magnetic powder cores of the present inventionexhibit stable soft magnetic characteristics. Moreover, the rate (ΔL) ofchange decreases only to approximately −25% in a DC bias magnetic fieldof 6,800 A/m, showing a superior soft magnetic characteristic.

[0480] Thus, these magnetic powder cores are preferably applicable tomagnetic core components requiring a constant permeability, such astransformer cores for switching power supplies and smoothing chokecores.

[0481] In contrast, in the magnetic powder core of COMPARATIVE EXAMPLE,the rate (ΔL) of change in inductance decreases to approximately −70%when the DC bias magnetic field is 6,800 A/m, showing a large variationin magnetic characteristics. Thus, magnetic components, such astransformers, using this magnetic powder core will exhibit inferiorcharacteristics.

Permeability and Core Loss of Magnetic Powder Core

[0482] The permeability and the core loss of three magnetic powderscores were measured. These magnetic powder cores were composed of glassyalloy powders having different particle sizes in the range of 38 μm orless, the range of more than 38 μm to 60 μm, and the range of more than60 μm to 100 μm. The amorphous volume fraction Vamo of each glassy alloywas determined by DSC.

[0483]FIGS. 19A, 19B, and 19C illustrate the dependence of thepermeability (μ′), the core loss (W_(0.5/200k)) and the core loss(W_(1/100k)), respectively, on the amorphous volume fraction of magneticpowder cores composed of glassy alloy powders, each having a particlesize in the range of more than 60 μm to 100 μm (points ▪), more than 38μm to 60 μm (points ), and 38 μm or less (points ▴).

[0484]FIG. 19A illustrates that the effective permeability of themagnetic powder core tends to increase as the amorphous volume fractionincreases and that the amorphous volume fraction increases as theparticle size of the glassy alloy powder decreases.

[0485]FIG. 19B shows the core loss (W_(0.5/200k)) which was measured ata frequency of 200 kHz and a saturation magnetic flux density of 0.05 T,and FIG. 19C shows the core loss (W_(1/100k)) which was measured at afrequency of 100 kHz and a saturation magnetic flux density of 0.1 T.

[0486] As shown in FIGS. 19B and 19C, the core losses (W_(0.5/200k),W_(1/100k)) of the magnetic powder core tends to increase with anincrease in the amorphous volume fraction, as in the effectivepermeability. Some magnetic powder cores having an amorphous volumefraction exceeding 85% exhibit a core loss (W_(1/100k)) of 700 kW/m³ orless.

[0487] Accordingly, it is preferable to use a glassy alloy powder havinga particle size of 38 μm or less in order to obtain a magnetic powdercore exhibiting superior effective permeability and core loss when theglassy alloy powder is prepared by a gas atomizing process. If a glassyalloy powder having a particle size exceeding 38 μm is used, it ispreferable that the particle size be smaller and the amorphous volumefraction be larger.

[0488] In particular, a core loss (W_(1/100k)) of the magnetic powdercore of 700 kW/m³ or less is achieved by an amorphous volume fraction of85% or more in the glassy alloy powder, and a core loss (W_(1/100k)) of400 kW/m³ or less is achieved by a particle size of 38 μm or less in theglassy alloy powder.

Example 3 Properties of Magnetic Powder Core containing Silicone Rubberas Insulating Material

[0489] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare an ingot having a compositionFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87). This ingot was melted in acrucible provided with an atomizing nozzle at 1,350° C. (which was atleast 140° C. higher than the melting point of the glassy alloy). Themelt was atomized together with gaseous argon with a pressure of 8.6 MPathrough the atomizing nozzle to prepare an alloy powder. The alloypowder was classified to prepare a glassy alloy powder having a particlesize of 62 μm or less.

[0490] Next, the glassy alloy powder was compounded with 0.67 to 4weight % silicone rubber as an insulating material. The mixture wascompressed to a molding pressure P_(s) of 1,500 MPa at room temperature(298 K (25° C.)) in a reduced pressure atmosphere of 6.6×10⁻³ Pa. Thecompressed mixture was annealed at 683 K (410° C.) for approximately 60minutes under this molding pressure P_(s). Magnetic powder cores(EXAMPLES 3-1 to 3-5) were prepared in such a manner. These magneticpowder cores were toroidal with an outer diameter of 12 mm, an innerdiameter of 6 mm, and a thickness of 2 mm.

[0491] Also, magnetic powder cores for comparison (COMPARATIVE EXAMPLES3-1 and 3-2) were prepared as in the above process, but epoxy resin andpolyimide resin were used as insulating materials, instead of thesilicone rubber.

[0492] The core loss (W_(1/100k)) of each magnetic powder core wasmeasured at a frequency of 100 kHz and a saturation magnetic fluxdensity of 0.01 T. Table 1 shows these results. TABLE 1 InsulatingMaterial Core Loss Content (W_(1/100k)) Type (weight %) (kW/m³) EXAMPLE3-1 Silicone Rubber 0.67 310 EXAMPLE 3-2 Silicone Rubber 1.33 290EXAMPLE 3-3 Silicone Rubber 2.0 230 EXAMPLE 3-4 Silicone Rubber 3.0 ≦200EXAMPLE 3-5 Silicone Rubber 4.0 300 COMPARATIVE Epoxy Resin 2.0 620EXAMPLE 3-1 COMPARATIVE Polyimide Resin 2.0 ≧2,000 EXAMPLE 3-2

[0493] Table 1 shows that all the magnetic powder cores of EXAMPLES 3-1to 3-5 using the silicone rubber as the insulating material exhibit acore loss (W_(1/100k)) of 310 kW/m³ or less, which is significantlylower than that of a conventional magnetic powder core. In particular,the magnetic powder core containing 3 weight % silicone rubber exhibitsa significantly low core loss of 200 kW/m³ or less.

[0494] The observed magnetostriction constants of the glassy alloys ofEXAMPLES 3-1 to 3-5 are in the range of 2×10⁻⁵ to 3×10⁻⁵, demonstratingextremely reduced internal stress in the magnetic powder cores.

[0495] In the magnetic powder cores of COMPARATIVE EXAMPLES 3-1 and 3-2,the core loss (W_(1/100k)) is higher than that of EXAMPLES 3-1 to 3-5.In particular, the magnetic powder core of COMPARATIVE EXAMPLE 3-2 usingthe polyimide insulating material exhibits a core loss (W_(1/100k)) of2,000 kW/m³ or more.

[0496] It is considered that the small core loss (W_(1/100k)) in themagnetic powder cores of EXAMPLES 3-1 to 3-5 is caused by small residualstress in the glassy alloy powder due to small hardening stress of thesilicone rubber. In contrast, the large core loss (W_(1/100k)) of themagnetic powder cores of COMPARATIVE EXAMPLES 3-1 and 3-2 is consideredto be caused by large internal stress due to large hardening stress,since these insulating materials are less elastic. In COMPARATIVEEXAMPLE 3-2, it is considered that the extremely large core loss iscaused by the accumulated internal stress due to significantly largehardening stress of the polyimide resin.

[0497] Accordingly, a magnetic powder core having extremely small coreloss is obtainable by compaction molding of a glassy alloy powder, whichis prepared by a gas atomizing process, and a silicone rubber at roomtemperature and annealing of the molded article.

[0498] As described above, the magnetic powder core of the presentinvention is a molded article of a mixture of a glassy alloy powder andan insulating material, and the glassy alloy powder has a textureprimarily composed of an amorphous phase and has a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature. The insulating material enhances theresistivity of the entire magnetic powder core and reduces core loss ofthe magnetic powder core due to reduced eddy current loss. Thus, areduction in permeability can be moderated in a high-frequency region.

[0499] A magnetic powder core using a glassy alloy having a resistivityof at least 1.5 μΩ•m exhibits lower core loss in a high-frequency regiondue to reduced eddy current loss in the glassy alloy particles.

[0500] In the method for making the magnetic powder core of the presentinvention, a magnetic core precursor is annealed at a temperature in therange between (T_(g)−170) K and T_(g) K. Thus, the internal stress ofthe magnetic core precursor is relieved without crystallization of theglassy alloy. Accordingly, a magnetic powder core having low coerciveforce can be produced by the method in accordance with the presentinvention.

Example 4 Heat Dissipation of Step-down Converter Circuit

[0501] A toroidal magnetic powder core composed of a glassy alloy havinga composition Fe₇₀Al₇P_(9.65)C_(2.3)B_(8.05)Si₃ was prepared as inExample 1, except that the molding pressure was 1,500 MPa and themolding temperature was room temperature (25° C. (298 K)). The magneticpowder core had an outer diameter of 18 mm, an inner diameter of 12 mm,and a thickness of 5 mm.

[0502] A coil was wound by seven turns around the magnetic powder coreto prepare a choking coil having an inductance of 2.9 μH.

[0503] This choking coil was used as a coil with a magnetic core tomount into a step-down converter circuit shown in FIG. 24 (EXAMPLE 4).This converter circuit had a transistor switching element, a dioderectification element, and an electrolytic capacitor with anelectrostatic capacitance of 33 μF. The input was a DC of 12 V, theoutput was a DC of 5 V and 25 A, and the switching frequency of theswitching element was 100 kHz. The heat dissipation of the choking coilwas measured. Table 2 shows the results.

[0504] Also, step-down converter circuits were assembled using a chokingcoils including a magnetic powder core of carbonyl iron powder(COMPARATIVE EXAMPLE 4-1) and a magnetic powder core of an FeAlSi alloy(COMPARATIVE EXAMPLE 4-2) as in EXAMPLE 4 to measure the heatdissipation of the choking coil. Table 2 also shows the result. TABLE 2Heat Dissipation (W) EXAMPLE 4 0.5 COMPARATIVE EXAMPLE 4-1 3.9COMPARATIVE EXAMPLE 4-2 1.1

[0505] As shown in Table 2, the choking coil of EXAMPLE 4 exhibits lowerheat dissipation compared to the choking coils of COMPARATIVE EXAMPLES4-1 and 4-2. Accordingly, the step-down converter circuit using thischoking coil exhibits high conversion efficiency due to reduced heatdissipation and low loss. Also, the magnetic core of EXAMPLE 2 will showsubstantially the same effect when it is used in the step-down convertercircuit.

[0506] As described above, the switching power supply of the presentinvention includes a transformer having a magnetic core composed of aglassy alloy powder. The internal stress of the magnetic core can berelieved by annealing at a temperature which is sufficiently lower thanthe crystallization temperature of the glassy alloy, and the heatdissipation from the entire switching power supply can be reduced due toreduced core loss.

[0507] The switching power supply of the present invention includes acoil with a magnetic core composed of a glassy alloy powder. Theinternal stress of the magnetic core can be relieved by annealing at atemperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the heat dissipation from theentire switching power supply can be reduced due to reduced core loss.

[0508] Each of the step-down converter circuit, boosting convertercircuit, and polarity-reversing converter circuit of the presentinvention uses a coil with a magnetic core composed of a glassy alloypowder. The internal stress of the magnetic core can be relieved byannealing at a temperature which is sufficiently lower than thecrystallization temperature of the glassy alloy, and the heatdissipation from the entire converter circuit can be reduced due toreduced core loss.

[0509] The active filter of the present invention uses a coil with amagnetic core composed of a glassy alloy powder in the converter circuittherein. Since this magnetic core exhibits low loss, the heatdissipation from the entire active filter can be reduced.

[0510] The magnetic core exhibiting low permeability does not require agap for preventing magnetic saturation, and does not generate a leakagemagnetic field which adversely affects other peripheral circuits.

Example 5 Magnetic Characteristics of Glassy Alloy

[0511] A glassy alloy powder having a compositionFe₇₇Al₁P_(9.23)C_(2.2)B_(7.7)Si_(2.87) was prepared as in EXAMPLE 4. Amixture of 97 parts by weight of glassy alloy powder and 3 part byweight of silicone elastomer as an insulating material was dried at 473K (200° C.) for 1 hour in air and was disintegrated. The mixture wasloaded into a tungsten carbide mold and was heated to a temperature of683 K under a pressure of 1,500 MPa in the discharge plasma sinteringapparatus of a reduced pressure atmosphere of 6.6×10⁻³ Pa. A toroidalmagnetic powder core with an outer diameter of 12 mm, an inner diameterof 6 mm, and a thickness of 2 mm was thereby prepared. The rate ofchange in amplitude permeability (Δμ′) and the core loss (W) of themagnetic powder core were measured (EXAMPLE 5). The results are shown inFIGS. 35 and 36.

[0512] The rate of change in amplitude permeability (Δμ′) and the coreloss (W) of a magnetic powder core of carbonyl iron powder were alsomeasured (COMPARATIVE EXAMPLE 5). The results are shown in FIGS. 35 and36.

[0513]FIG. 36 shows the relationship between the rate of change inamplitude permeability (Δμ′) relative to the amplitude permeability in amagnetic field of 200 A/m and the magnetic field. The magnetic core ofEXAMPLE 5 exhibits a rate of change in amplitude permeability ofapproximately −5% in a magnetic field of 2,000 A/m, that is, exhibitssubstantially the same amplitude permeability regardless of the magneticfield.

[0514] In contrast, the magnetic core of COMPARATIVE EXAMPLE 5 exhibitsa rate of change in amplitude permeability exceeding +5% in a magneticfield of 2,000 A/m, that is, exhibits a significant change in amplitudepermeability with a change in magnetic field.

[0515]FIG. 35 shows the dependence of the core loss (W) measured at amagnetic flux density Bm of 0.1 T on the frequency. The magnetic core ofpresent invention exhibits a relatively small core loss (W) ofapproximately 10 kWm⁻³ at a frequency of 10 kHz, and a core loss (W) ofapproximately 250 kWm⁻³.

[0516] In contrast, the magnetic core of COMPARATIVE EXAMPLE 5 exhibitsa considerably high core loss (W) of 250 kWm⁻³ at a frequency of 10 kHz,520 kWm⁻³ at a frequency of 20 kHz, and 2,000 kWm⁻³ at a frequency of100 kHz (not shown in the drawing).

[0517] The magnetic core composed of the glassy alloy according to thepresent invention exhibits smaller core loss compared to theconventional carbonyl iron powder magnetic core and exhibits constantamplitude permeability over a wide range of magnetic field.

[0518] When the magnetic core of the present invention is used as amagnetic core of a filter, the filter exhibits reduced loss and reducedheat dissipation, and outputs smoothed waveforms with less distortion.

[0519] As described above, the filter of the present invention includesa capacitor and an inductor of a coil wound around a magnetic core. Themagnetic core is composed of a glassy alloy powder having a temperaturedifference ΔT_(x) in a supercooled liquid and an insulating material.The internal stress of the glassy alloy can be relieved by annealing ata temperature which is sufficiently lower than the crystallizationtemperature of the glassy alloy, and the magnetic core exhibits low coreloss and a substantially constant amplitude permeability over a wideintensity range of magnetic field. Thus, the filter exhibits reducedheat dissipation and outputs less distorted waveforms.

[0520] Since a glassy alloy having a resistivity of at least 1.5 μΩ•m isused, the resulting magnetic core shows further reduced core loss due toreduced eddy current loss in the glassy alloy particles in ahigh-frequency region. Accordingly, the filter exhibits furtherdecreased loss.

[0521] Moreover, the insulating material increases the resistivity ofthe magnetic core, resulting in decreased core loss due to reduced eddycurrent loss. Moreover, a reduction in permeability in a high-frequencyregion is suppressed. Thus, the filter exhibits improved high-frequencycharacteristics.

[0522] Since the rate of change in amplitude permeability of themagnetic core in a magnetic field of 2,000 A/m is within ±10 of anamplitude permeability in a magnetic field of 200 A/m, the filteroutputs less distorted waveforms. Thus, the filter is preferablyapplicable to a smoothing circuit of a pulse width modulating amplifier.

[0523] Since the permeability of the magnetic core at 100 kHz is in therange of 50 to 200, the number of turns of the coil can be reduced,resulting in miniaturization of the inductor and thus the filter.

[0524] The magnetic core of the filter of the present invention iscomposed of a glassy alloy having a predetermined composition, exhibitssmaller core loss compared with a conventional carbonyl iron powdermagnetic core, and exhibits constant amplitude permeability over a wideintensity range of magnetic field. Thus, the filter exhibits reducedheat dissipation due to reduced loss and outputs smoothed waveforms withless distortion.

[0525] The amplifying device of the present invention includes anamplifier for outputting a pulsed current and a filter, for smoothingthe pulsed current, in connection with the output side of the amplifier.The filter includes a capacitor and an inductor of coil wound around themagnetic core. Thus, the amplifying device exhibits reduced heatdissipation due to low loss and outputs waveforms with less distortion.

Example 6 Dependence of Physical and Magnetic Properties on P, Si, C,and B Contents

[0526] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt in a high-frequency induction heating apparatus in areduced-pressure Ar atmosphere to prepare ingots having differentcompositions. Each ingot was melted in a crucible and was jetted onto arotating roller through a nozzle in a reduced-pressure Ar atmosphere bya single-roller process to quench the melt and to form a glassy alloytape, of an amorphous texture, with a width of 1 mm and a thickness of20 μm. Amorphous soft-magnetic alloy tapes of EXAMPLES 6-1 to 6-14 wereprepared in such a manner.

[0527] A Ga-containing amorphous soft-magnetic alloy tape represented byFe₇₀Al₅Ga₂P_(9.65)C_(5.75)B_(4.6)Si₃ was prepared for comparison(COMPARATIVE EXAMPLE 6)

[0528] Table 3 shows the compositions of the resulting amorphoussoft-magnetic alloy tapes of the present invention. The compositions arerepresented by Fe₇₀Al₇(P_(0.76)Si_(0.24))_(v)C_(z)B_(w), wherein v is inthe range of 10.35 to 14.95 atomic percent, Z is in the range of 1.15 to8.05 atomic percent, and w is in the range of 2.3 to 9.2 atomic percent.

[0529] The amorphous soft-magnetic alloys of EXAMPLES 6-1 to 6-14 weresubjected to crystallographic analysis by X-ray diffractometry. FIG. 37shows the results.

[0530] The amorphous soft-magnetic alloys of EXAMPLES 6-4 and 6-14 andCOMPARATIVE EXAMPLE 6 were subjected to DSC at a heating rate of 0.67K/sec. FIG. 38 and Table 4 show the DSC results. TABLE 3 AlloyComposition EXAMPLE 6-1 Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(5.7)B_(4.6)EXAMPLE 6-2 Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(5.7)B_(4.6) EXAMPLE 6-3Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(5.7)B_(6.9) EXAMPLE 6-4Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.4)B_(6.9) EXAMPLE 6-5Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(3.4)B_(4.6) EXAMPLE 6-6Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(5.7)B_(2.3) EXAMPLE 6-7Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(8.0)B_(2.3) EXAMPLE 6-8Fe₇₀Al₇(P_(0.76)Si_(0.24))_(10.35)C_(3.4)B_(9.2) EXAMPLE 6-9Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(1.1)B_(9.2) EXAMPLE 6-10Fe₇₀Al₇(P_(0.76)Si_(0.24))_(14.95)C_(1.1)B_(6.9) EXAMPLE 6-11Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(4.6)B_(5.75) EXAMPLE 6-12Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(4.6)B_(6.9) EXAMPLE 6-13Fe₇₀Al₇(P_(0.76)Si_(0.24))_(11.5)C_(3.4)B_(8.05) EXAMPLE 6-14Fe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(2.3)B_(8.05)

[0531] TABLE 4 T_(g) (K) T_(x) (K) ΔT_(x) (K) EXAMPLE 6-4 758 821 63EXAMPLE 6-14 760 821 61 COMPARATIVE 740 800 60 EXAMPLE 6

[0532]FIG. 37 demonstrates that the amorphous soft-magnetic alloy tapesof EXAMPLES 6-1 to 6-14 exhibit broad X-ray diffraction patterns whichare assigned to amorphous textures.

[0533]FIG. 38 and Table 4 demonstrate that the amorphous soft-magneticalloy of EXAMPLE 6-4 has a glass transition temperature T_(g) at 758 Kand a crystallization temperature T_(x) at 821 K, thus the temperaturedifference ΔT_(x), represented by ΔT_(x)=T_(x)−T_(g), in the supercooledliquid being 63 K. The amorphous soft-magnetic alloy of EXAMPLE 6-14 hasa glass transition temperature T_(g) of 760 K and a crystallizationtemperature T_(x) of 821° C., thus the temperature difference ΔT_(x),represented by ΔT_(x)=T_(x)−T_(g), in the supercooled liquid being 60 K.

[0534] The amorphous soft-magnetic alloy of COMPARATIVE EXAMPLE 6 has aglass transition temperature T_(g) at 740 K and a crystallizationtemperature T_(x) at 800 K, thus the temperature difference ΔT_(x),represented by ΔT_(x)=T_(x)−T_(g), in the supercooled liquid being 60 K.

[0535] The amorphous soft-magnetic alloys of EXAMPLES 6-4 and 6-14 haveeach a wide supercooled liquid region below the crystallizationtemperature T_(x) regardless of the Ga-free composition and a largeΔT_(x) (=T_(x)−T_(g)) as a glassy alloy. Thus, the alloy consisting ofFe, Al, P, C, B, and Si has a large temperature difference ΔT_(x) of atleast 20 K in a supercooled liquid.

[0536] The amorphous soft-magnetic alloy tapes of EXAMPLES 6-1 to 6-14were subjected to DSC at a heating rate of 0.67 K/sec to measure theglass transition temperature T_(g), the crystallization temperatureT_(x), the Curie temperature T_(c), and the melting point T_(m) and todetermine the temperature difference ΔT_(x) in a supercooled liquid andthe ratio T_(g)/T_(m).

[0537]FIG. 39 shows the dependence of the glass transition temperatureT_(g) on the composition, FIG. 40 shows the dependence of thecrystallization temperature T_(x) on the composition, FIG. 41 shows thedependence of the temperature difference ΔT_(x) in a supercooled liquidon the composition, FIG. 42 shows the dependence of the melting pointT_(m) on the on composition, FIG. 43 shows the dependence of the ratioT_(g)/T_(m) on the composition, and FIG. 44 shows the dependence of theCurie temperature T_(c) on the composition.

[0538] The saturation magnetization (σs) by a VSM (vibrating samplemagnetometer) and the permeability (μe) and coercive force (Hc) by a BHloop tracer were measured for the amorphous soft-magnetic alloy tapes ofEXAMPLES 6-1 to 6-14.

[0539]FIG. 45 shows the dependence of the saturation magnetization (σs)on the composition, FIG. 46 shows the dependence of the permeability(μe) on the composition, and FIG. 47 shows the dependence of thecoercive force (Hc) on the composition.

[0540] Figures attached to the plots in the ternary diagrams in FIGS. 39to 47 represent the glass transition temperature T_(g), thecrystallization temperature T_(x), the temperature difference ΔT_(x) inthe supercooled liquid, melting point T_(m), the ratio T_(g)/T_(m), theCurie point T_(c), the saturation magnetization (σs), the permeability(μe), and the coercive force (Hc), respectively.

[0541] In FIGS. 39 to 47, a figure shown in the vicinity of eachisothermal line or isoline represents the temperature or the valuethereof.

[0542]FIG. 39 illustrates that the glass transition temperature T_(g)increases with an increased B content and a decreased C content. Theisothermal line at T_(g)=760 K lies in a region defined by the B contentw in the range of 4.1 atomic percent to 8.05 atomic percent and by the Ccontent z in the range of 2.3 atomic percent to 5.1 atomic percent.

[0543]FIG. 40 illustrates the crystallization temperature T_(x)increases with an increased B content and a decreased C content, as inthe T_(g). The isothermal line at T_(x)=815 K lies in a region definedby the B content w in the range of 4 atomic percent to 8.4 atomicpercent and by the C content z in the range of 0.3 atomic percent to 5atomic percent.

[0544] As shown in FIG. 41, the region surrounded by the isothermal lineat T_(g)=760 K shown in FIG. 39 and the isothermal line at T_(x)=815 Kcorresponds to the isothermal line at ΔT_(x)=60 K. The temperaturedifference ΔT_(x) in the supercooled liquid exceeds 60 K within thisrange. In particular, the amorphous soft-magnetic alloyFe₇₀Al₇(P_(0.76)Si_(0.24))_(12.65)C_(3.45)B_(6.9) of EXAMPLE 6-4exhibits a temperature difference ΔT_(x) of 63 K.

[0545]FIG. 42 illustrates that the melting point T_(m) exhibits themaximum of 1,361 K at a higher-B-content side and the minimum of 1,226 Kat a lower-B-content side of the isothermal line at 1,290 K. Since thedifference between the maximum and the minimum is 135 K, the meltingpoint T_(m) of this amorphous soft-magnetic alloy is sensitive to the Bcontent w.

[0546] With reference to FIG. 43, the high sensitivity of the meltingpoint T_(m) to the composition affects the dependence of the ratioT_(g)/T_(m) on the composition. The ratio T_(g)/T_(m) slightly increasesa lower-B-content side of the isoline at T_(g)/T_(m)=0.6, which liesalong a B content of 5.75 atomic percent. A large ratio T_(g)/T_(m)means a decreased temperature difference ΔT_(x) between the meltingpoint T_(m) and the glass transition temperature T_(g). Thus, an alloyhaving a composition within this range has enhanced amorphousformability even the cooling rate is decreased; that is, the criticalcooling rate is low. Accordingly, the larger T_(g)/T_(m), the higheramorphous formability.

[0547] Comparing FIG. 43 with FIG. 41, the region of T_(g)/T_(m) of 0.60or less in FIG. 43 overlaps with the region of ΔT_(x) of 60 K or more inFIG. 41. Thus, a high T_(g)/T_(m) region does not always overlap with ahigh ΔT_(x) region. The T_(g)/T_(m), however, is as relatively high as0.57 to 0.58 even in a region of ΔT_(x) of 60 K or more. Thus, thisamorphous soft-magnetic alloy within this range exhibits relatively highamorphous formability.

[0548]FIG. 44 illustrates that the Curie temperature T_(c) increaseswith a decreased total content of P and Si. FIG. 45 illustrates that thesaturation magnetization (σs) also increases with a decreased totalcontent of P and Si. At a total content of 12.65 atomic percent or less,the saturation magnetization (σs) is 180×10⁻⁶ (Wb•m•kg⁻¹) or more. At atotal content of 11.5 atomic percent or less, the saturationmagnetization (σs) is 190×10⁻⁶ (Wb•m•kg⁻¹) or more. Thus, the amorphoussoft-magnetic alloy of the present invention exhibits a high saturationmagnetization (σs).

[0549] As described above, the Curie temperature T_(c) is highlycorrelated with the saturation magnetization (σs). Accordingly, anoptimized composition increases both the Curie temperature T_(c) and thesaturation magnetization (σs) and the resulting amorphous soft-magneticalloy exhibits high thermal stability of magnetic characteristics due tothe increased Curie temperature T_(c).

[0550]FIG. 46 shows a maximum permeability (μe) of 28,300, but does notshow nor suggest a clear relationship between the composition and thepermeability (μe). Thus, it is considered that the dependence of thepermeability (μe) on the P, C, B, and Si contents is not significant.

[0551]FIG. 47 illustrates that the coercive force (Hc) does not show aclear dependence on the P, C, B, and Si contents, unlike the saturationmagnetization (σs) and the above thermal properties.

[0552] Accordingly, the thermal properties T_(g), T_(x), ΔT_(x), T_(m),T_(g)/T_(m), T_(c) and the saturation magnetization (σs) show highdependence on the P, C, B, and Si contents.

Example 7 Dependence of Physical and Magnetic Properties on Fe and AlContents

[0553] Melts prepared by melting ingots having different compositionwere sprayed onto a rotating roller in a reduced-pressure atmosphere asin EXAMPLE 6 to prepare amorphous soft-magnetic alloy tapes with a widthof 1 mm and a thickness of 20 μm of EXAMPLES 7-15 to 7-18. Theseamorphous soft-magnetic alloys had compositions represented byFe_(100-x-y)Al_(x)(P_(0.42)C_(0.1)B_(0.35)S_(0.13))_(y) wherein x was 1to 5 atomic percent and y was 18 to 22 atomic percent. Table 5 shows thecompositions of the resulting amorphous soft-magnetic alloy tapes. FIG.48 illustrates X-ray diffraction patterns of the resulting amorphoussoft-magnetic alloy. TABLE 5 Alloy Composition EXAMPLE 7-15Fe₇₇Al₅(P_(0.42)C_(0.01)B_(0.35)Si_(0.13))₁₈ EXAMPLE 7-16Fe₇₇Al₃(P_(0.42)C_(0.01)B_(0.35)Si_(0.13))₂₀ EXAMPLE 7-17Fe₇₇Al₁(P_(0.42)C_(0.01)B_(0.35)Si_(0.13))₂₂ EXAMPLE 7-18Fe₇₉Al₁(P_(0.42)C_(0.01)B_(0.35)Si_(0.13))₂₀

[0554]FIG. 48 demonstrates that the amorphous soft-magnetic alloy tapesof EXAMPLES 7-15 to 7-18 exhibit broad X-ray diffraction patterns whichare assigned to amorphous textures.

[0555] The amorphous soft-magnetic alloy tapes of EXAMPLES 7-15 to 7-18were subjected to DSC at a heating rate of 0.67 K/sec to determine theglass transition temperature T_(g), the crystallization temperatureT_(x), the Curie temperature T_(c), and the melting point T_(m), thetemperature difference ΔT_(x) in a supercooled liquid, and the ratioT_(g)/T_(m).

[0556]FIG. 49 shows the dependence of the glass transition temperatureT_(g) on the composition, FIG. 50 shows the dependence of thecrystallization temperature T_(x) on the composition, FIG. 51 shows thedependence of the temperature difference ΔT_(x) in a supercooled liquidon the composition, FIG. 52 shows the dependence of the melting pointT_(m) on the composition, FIG. 53 shows the dependence of the ratioT_(g)/T_(m) on the composition, and FIG. 54 shows the dependence of theCurie temperature T_(c) on the composition.

[0557] The saturation magnetization (σs) by VSM and the permeability(μe) and the coercive force (Hc) by a BH loop tracer were measured forthe amorphous soft-magnetic alloy tapes of EXAMPLES 7-15 to 7-18.

[0558]FIG. 55 shows the dependence of the saturation magnetization (σs)on the composition, FIG. 56 shows the dependence of the permeability(μe) on the composition, and FIG. 57 shows the dependence of thecoercive force (Hc) on the composition.

[0559] Figures attached to the plots in the ternary diagrams in FIGS. 49to 57 represent the glass transition temperature T_(g), thecrystallization temperature T_(x), the temperature difference ΔT_(x) inthe supercooled liquid, melting point T_(m), the ratio T_(g)/T_(m), theCurie point T_(c), the saturation magnetization (σs), the permeability(μe), and the coercive force (Hc).

[0560] In FIGS. 49 to 57, a figure shown in the vicinity of eachisothermal line or isoline represents the temperature or the valuethereof.

[0561]FIG. 49 illustrates that the glass transition temperature T_(g)increases with an increased total (PCBSi) content and a decreased Fe orAl content. The isothermal line at T_(g)=760 K lies along a line of thetotal (PCBSi) content y of approximately 21 atomic percent.

[0562]FIG. 50 illustrates the crystallization temperature T_(x)increases with an increased total (PCBSi) content and a decreased Fe orAl content, as in the T_(g). The isothermal line at T_(x)=800 K liesalong a line of the (PCBSi) content y of approximately 21 atomicpercent.

[0563] As shown in FIG. 51, the temperature difference ΔT_(x) increaseswith an increased total (PCBSi) content and a decreased Fe or Alcontent. The isothermal line at ΔT_(x)=35 K lies in the vicinity of atotal (PCBSi) content y of 20 to 22 atomic percent and in the vicinityof an Fe content of 75 to 78 atomic percent. Thus, the temperaturedifference ΔT_(x) in a supercooled liquid exceeds 35 K within the rangeof the total content y of 20 atomic percent or more and the Fe contentof 78 atomic percent or less. In particular, the amorphous soft-magneticalloy Fe₇₇Al₁(P_(0.42)C_(0.1)B_(0.35)Si_(0.13))₂₂ of EXAMPLE 7-17exhibits a temperature difference ΔT_(x) of 37 K.

[0564] The temperature difference ΔT_(x) shown in FIG. 41 is larger thanthat shown in FIG. 51. This difference is probably due to a differencein the composition between EXAMPLE 6 and EXAMPLE 7. The amorphoussoft-magnetic alloy shown in FIG. 41 has an Al content of 7 atomicpercent, which is higher than the Al content (1 to 5 percent) in theamorphous soft-magnetic alloy shown in FIG. 51. Moreover, the amorphoussoft-magnetic alloy shown in FIG. 41 has an Fe content of 70 atomicpercent, which is lower than the Fe content (77 to 79 atomic percent) inthe amorphous soft-magnetic alloy shown in FIG. 51. Such differences inthe composition are considered to affect the temperature differenceΔT_(x). Thus, the temperature difference ΔT_(x) tends to increase withan increase in Al content and with a decrease in Fe content.

[0565]FIG. 52 illustrates that the melting point T_(m) exhibits themaximum of 1,339 K at a higher-Fe-content side and the minimum of 1,282K at a lower-Fe-content side of the isothermal line at 1,300 K. Thus,the difference between the maximum and the minimum is 57 K, which issmaller than the difference 135 K in FIG. 42. Accordingly, the meltingpoint T_(m) of this amorphous soft-magnetic alloy is less sensitive tothe Fe content, compared to the B content.

[0566] With reference to FIG. 53, the sensitivity of the melting pointT_(m) to the composition affects the dependence of the ratio T_(g)/T_(m)on the composition. The ratio T_(g)/T_(m) slightly increases alower-Fe-content side of the isoline at T_(g)/T_(m)=0.58, which lieswithin the range of Fe content of 76 to 78 atomic percent. A large ratioT_(g)/T_(m) means a decreased temperature difference ΔT_(x) between themelting point T_(m) and the glass transition temperature T_(g). Thus, analloy having a composition within this range has enhanced amorphousformability even the cooling rate is decreased; that is, the criticalcooling rate is low. Accordingly, the larger T_(g)/T_(m), the higheramorphous formability.

[0567] Comparing FIG. 53 with FIG. 51, the region of T_(g)/T_(m) of 0.58in FIG. 53 overlaps with the region of ΔT_(x) of 35 K in FIG. 51. Thus,a high T_(g)/T_(m) region overlaps with a high ΔT_(x) region. Thus, thisamorphous soft-magnetic alloy has a temperature difference ΔT_(x) of atleast 35 K and exhibits enhanced amorphous formability by decreasing theFe content.

[0568]FIG. 54 illustrates that the Curie temperature T_(c) increaseswith an increased total (PCBSi) content and a decreased Al content. FIG.55 illustrates that the saturation magnetization (σs) also increaseswith an increased total (PCBSi) content and a decreased Al content.

[0569] The Curie temperature T_(c) is highly correlated with thesaturation magnetization (σs). That is, the Curie temperature T_(c) andthe saturation magnetization (σs) increase by increasing the total(PCBSi) content and decreasing the Al content. Furthermore, theincreased Curie temperature T_(c) contributes to improved thermalstability of magnetic characteristics of the amorphous soft-magneticalloy.

[0570]FIG. 56 illustrates that the permeability (μe) tends to increaseas the Fe or Al content decreases. Also, FIG. 56 illustrates a maximumpermeability (μe) of 27,000 at an Fe content of 77 atomic percent and anAl content of 3 atomic percent.

[0571] The permeabilities (μe) of EXAMPLES 7-16 AND 7-18 having the sametotal (PCBSi) content of 20 atomic percent are 27,000 and 19,000,respectively, which are significantly different from each other. Thus,it is considered that the dependence of the permeability (μe) on thetotal (PCBSi) content is not significant, as in FIG. 46.

[0572]FIG. 57 illustrates that the coercive force (Hc) tends to increaseas the Fe content increases and the total (PCBSi) content decreases. Thedifference in the coercive force is, however, small and does not show aclear dependence on the composition, unlike the above thermalproperties.

[0573] Accordingly, the thermal properties T_(g), T_(x), ΔT_(x), T_(m),T_(g)/T_(m), T_(c) show high dependence on the Fe and Al contents,whereas the magnetic characteristics including the saturationmagnetization (σs) does not show clear dependence.

Example 8 Manufacturing of Injection-Molding Article

[0574] Predetermined amounts of Fe, Al, an Fe—C alloy, an Fe—P alloy, B,and Si were melt. The melt was injected into a mold shown in FIG. 1 toprepare a toroidal injection-molding article (EXAMPLE 8-19) of anamorphous soft-magnetic alloy as shown in FIG. 3. The resultinginjection-molding article had an outer diameter of 6 mm, an innerdiameter of 4 mm, and a thickness of 1 mm and had a composition ofFe₇₀Al₇P_(9.65)C_(3.45)B_(6.9)Si₃ which was the same as that in EXAMPLE6-4.

[0575] An injection-molding article of COMPARATIVE EXAMPLE 8-1 having anouter diameter of 6 mm, an inner diameter of 4 mm, and a thickness of 1mm and having a composition of Fe₇₀Al₅Ga₂P_(9.65)C_(5.75)B_(4.6)Si₃ wasproduced as in Example 8-19 This amorphous soft-magnetic alloy had thesame composition as that of the amorphous soft-magnetic alloy ofCOMPARATIVE EXAMPLE 6.

[0576] The resulting injection-molding articles were subjected to X-raydiffractometry and DSC at a heating rate of 0.67 K/sec. The results areshown in FIGS. 25 and 26.

[0577]FIG. 58 illustrates that the injection-molding article of EXAMPLE8-19 has a broad X-ray diffraction pattern which is assigned to anamorphous phase. FIG. 59 illustrates that the DSC thermogram has a glasstransition temperature T_(g) at 760 K and a crystallization temperatureT_(x) at 822 K, thus the temperature difference ΔT_(x) in a supercooledliquid being 62 K.

[0578] As described above, the injection-molding article of EXAMPLE 8-19has a wide supercooled liquid region below the crystallizationtemperature T_(x) regardless of the Ga-free composition and a largeΔT_(x) (=T_(x)−T_(g)) as a glassy alloy.

[0579] The injection-molding articles of EXAMPLE 8-19 and COMPARATIVEEXAMPLE 8-2 were annealed at 698 K for 30 minutes. B-H curves ofunannealed articles and annealed articles were measured. The results areshown in FIG. 60 to 63. Moreover, the magnetic characteristics of thesearticles are shown in Table 6 in which the magnetization B₈₀₀ indicatesa magnetization in an external magnetic field of 800 A/m. TABLE 6 Co-Re- Remanence ercive manence Mag- Magnet- Force Ratio netization izationHc Br/ Br (T) B₈₀₀ (T) (A/m) B₈₀₀ EXAMPLE Unannealed 0.28 0.605 2.790.463 8-19 Annealed 0.38 0.990 1.83 0.384 COM- Unannealed 0.31 0.6657.96 0.466 PARATIVE EXAMPLE Annealed 0.02 0.995 4.00 0.020 8-2

[0580]FIGS. 60 and 61 show B-H curves of the unannealed and annealedarticles, respectively, of EXAMPLE 8-19. FIGS. 60 and 61 and Table 6demonstrate that the remanence magnetization (Br) and the magnetization(B₈₀₀) of the injection-molding article of EXAMPLE 8-19 increase byannealing, whereas the coercive force (Hc) decreases. Thus, the softmagnetic characteristics are improved by annealing. It is consideredthat the internal stress in the injection-molding article is relievedwithout precipitation of a crystalline phase during annealing.

[0581]FIGS. 62 and 63 show B-H curves of the unannealed and annealedarticles, respectively, of COMPARATIVE EXAMPLE 8-2. FIGS. 62 and 63 andTable 6 demonstrate that the magnetization (B₈₀₀) of theinjection-molding article of COMPARATIVE EXAMPLE 8-2 increases byannealing, whereas the remanence magnetization (Br) significantlydecreases and the coercive force (Hc) increases. Thus, the soft magneticcharacteristics are impaired by annealing. It is considered that acrystalline phase precipitates during annealing and the internal stressincreases in the injection-molding article, although no diffractionpatterns suggesting an amorphous phase were observed by X-raydiffractometry of this injection molding article.

[0582] Although no crystalline phases are identified, the grounds forthe assumption of the crystalline phase precipitation are as follows.

[0583] First, the amorphous soft-magnetic alloy of the injection-moldingarticle of COMPARATIVE EXAMPLE 8-2 is inferior in amorphous formabilityto the amorphous soft-magnetic alloy of the injection-molding article ofEXAMPLE 8-19. Thus, the regularity of the atomic arrangement in thetexture of the alloy of COMPARATIVE EXAMPLE 8-2 is higher than that ofEXAMPLE 8-19. As a result, a crystalline phase readily precipitatesduring annealing.

[0584] Second, it is considered that a slight amount of crystallinephase is formed or nuclei facilitating the crystal growth are formed dueto low amorphous formability of the amorphous soft-magnetic alloy ofCOMPARATIVE EXAMPLE 8-2 and crystallization from these nuclei occursduring annealing.

[0585] The reason that no crystalline phases are observed by X-raydiffractometry in COMPARATIVE EXAMPLE 8-2 is as follows. The crystallinephase precipitates into part of the texture and thus is not detected bythe X-ray diffractometry due to insufficient detection sensitivity.

[0586] As described above, the amorphous soft-magnetic alloy of thepresent invention exhibits high amorphous formability which facilitatesthe formation of a perfect amorphous phase by quenching an alloy melt.Thus, the internal stress occurring during the quenching process can berelieved without precipitation of a crystalline phase during annealing.As a result, the amorphous soft-magnetic alloy exhibits improved softmagnetic characteristics which are not achieved by conventional glassyalloys.

[0587] Since the amorphous soft-magnetic alloy of the present inventioncontains Fe as a magnetic element and Al, P, C, B, and Si havingamorphous formability, this alloy is primarily composed of an amorphousalloy and exhibits superior soft magnetic characteristics. Since Alenhances the amorphous formability, the entire texture can be composedof a perfect amorphous phase.

[0588] Since this amorphous soft-magnetic alloy has a large temperaturedifference ΔT_(x) of at least 20 K in a supercooled liquid, an amorphousphase can be formed from a melt at a relatively low cooling rate. Thus,a bulk alloy which is thicker than a tape can be produced. Inparticular, a bulk casting or injection molding article can be formed bya casting or injection process using a melt of an alloy.

[0589] This amorphous soft-magnetic alloy exhibits high amorphousformability compared to the conventional Fe—Al—Ga—C—P—Si—B alloy. Sincea perfect amorphous phase can be formed at a decreased cooling rate, abulk alloy having a relatively large size and containing an amorphousphase can be produced by a casting process.

[0590] Since the entire texture is composed of a complete amorphousphase, the amorphous soft-magnetic alloy exhibits significantly improvedpermeability and saturation magnetization, resulting in superior softmagnetic characteristics.

[0591] The internal stress in the amorphous soft-magnetic alloy can berelieved under an appropriate condition without precipitation of acrystalline phase due to the complete amorphous phase, and the softmagnetic characteristics are further improved.

What is claimed is:
 1. A magnetic powder core comprising a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, the glassy alloy comprising Fe and at least one elementselected from Al, P, C, Si, and B, having a texture primarily composedof an amorphous phase, and exhibiting a temperature difference ΔT_(x),which is represented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20K in a supercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.
 2. Amagnetic powder core according to claim 1 , wherein the glassy alloy hasa resistivity of at least 1.5 μΩ•m.
 3. A magnetic powder core accordingto claim 1 , wherein the magnetic powder has a coercive force of 80 A/mor less in an applied magnetic field of ±2.4 kA/m.
 4. A magnetic powdercore according to claim 1 , wherein the magnetic powder has a coerciveforce of 40 A/m or less in an applied magnetic field of ±2.4 kA/m.
 5. Amagnetic powder core according to claim 1 , wherein the magnetic powdercore has a core loss of 400 kW/m³ or less under the conditions of afrequency of 100 kHz and a magnetic flux density of 0.1 T.
 6. A magneticpowder core according to claim 1 , wherein the insulating materialcomprises a silicone rubber.
 7. A magnetic powder core according toclaim 1 , wherein the glassy alloy is represented by the followingformula:(Fe_(1-a)T_(a))_(100-x-v-z-w)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w) whereinT represents at least one element of Co and Ni, and the subscripts a, b,x, v, z, and w satisfy the relationships, 0≦a≦0.15 by atomic ratio,0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomic percent, 0 atomicpercent<v≦22 atomic percent, 0 atomic percent<z≦12 atomic percent, and 0atomic percent<w≦16 atomic percent.
 8. A method for making a magneticpowder core comprising: a powder preparation step of preparing a powderof a glassy alloy comprising Fe and at least one element selected fromAl, P, C, Si, and B, having a texture primarily composed of an amorphousphase, and exhibiting a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature; amolding step of mixing the glassy alloy powder with an insulatingmaterial and compacting the mixture to form a magnetic core precursor;and an annealing step of annealing the magnetic core precursor at atemperature in the range between (T_(g)−170) K and T_(g) K to relievethe internal stress of the magnetic core precursor.
 9. A method formaking a magnetic powder core according to claim 8 , wherein themagnetic core precursor is annealed at a temperature between (T_(g)−160)K and (T_(g)−50) K in the annealing step.
 10. A method for making amagnetic powder core according to claim 8 , wherein the magnetic coreprecursor is annealed at a temperature between (T_(g)−140) K and(T_(g−)60) K in the annealing step.
 11. A method for making a magneticpowder core according to claim 8 , wherein the magnetic core precursoris annealed at a temperature between (T_(g)−110) K and (T_(g)−60) K inthe annealing step.
 12. A method for making a magnetic powder coreaccording to claim 8 , wherein the glassy alloy is represented by thefollowing formula:(Fe_(1-a)T_(a))_(100-x-v-z-w)Al_(x)(P_(1-b)Si_(b))_(v)C_(z)B_(w) whereinT represents at least one element of Co and Ni, and the subscripts a, b,x, v, z, and w satisfy the relationships, 0≦a≦0.15 by atomic ratio,0<b≦0.8 by atomic ratio, 0 atomic percent<x≦20 atomic percent, 0 atomicpercent<v≦22 atomic percent, 0 atomic percent<z≦12 atomic percent, and 0atomic percent<w≦16 atomic percent.
 13. A switching power supplycomprising: a switching element for converting a DC voltage into arectangular waveform voltage; a transformer for transforming therectangular waveform voltage; and a rectification circuit and asmoothing circuit for converting the transformed rectangular waveformvoltage into a DC voltage; wherein the transformer comprises a magneticcore comprising a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy powder having a textureprimarily composed of an amorphous phase and exhibiting a temperaturedifference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.
 14. A switching power supply comprising: aswitching element for converting a DC voltage into a rectangularwaveform voltage; a transformer for transforming the rectangularwaveform voltage; and a rectification circuit and a smoothing circuitfor converting the transformed rectangular waveform voltage into a DCvoltage; wherein the smoothing circuit comprises a capacitor and a coilprovided with a magnetic core, the magnetic core comprising a moldedarticle of a mixture of a glassy alloy powder and an insulatingmaterial, the glassy alloy powder comprising Fe and at least one elementselected from Al, P, C, Si, and B, having a texture primarily composedof an amorphous phase, and exhibiting a temperature difference ΔT_(x),which is represented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20K in a supercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.
 15. Astep-down converter circuit comprising: a switching element; a coilprovided with a magnetic core generating a back electromotive force whenthe switching element breaks a DC current; a capacitor for smoothing acurrent generated by the back electromotive force; and a rectifyingelement connected to the coil provided with the magnetic core in anantiparallel state, the rectifying element, the coil provided with themagnetic core, and the capacitor constituting a circulating currentpath; wherein the magnetic core comprises a molded article of a mixtureof a glassy alloy powder and an insulating material, the glassy alloyhaving a texture primarily composed of an amorphous phase and exhibitinga temperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.
 16. A boosting converter circuitcomprising: a switching element; a coil provided with a magnetic coregenerating a back electromotive force when the switching element breaksa DC current; a rectifying element connected in series in the forwarddirection to the coil provided with the magnetic core for rectifying acurrent generated by the back electromotive force; and a capacitor forsmoothing the rectified current; wherein the magnetic core comprises amolded article of a mixture of a glassy alloy powder and an insulatingmaterial, the glassy alloy having a texture primarily composed of anamorphous phase and exhibiting a temperature difference ΔT_(x), which isrepresented by the equation ΔT_(x)=T_(x)−T_(g), of at least 20 K in asupercooled liquid, wherein T_(x) indicates the crystallizationtemperature and T_(g) indicates the glass transition temperature.
 17. Apolarity-reversing converter circuit comprising: a switching element; acoil provided with a magnetic core generating a back electromotive forcewhen the switching element breaks a DC current; a capacitor forsmoothing a current generated by the back electromotive force; and arectifying element connected in series in the backward direction to thecoil provided with the magnetic core for blocking the DC current;wherein the magnetic core comprises a molded article of a mixture of aglassy alloy powder and an insulating material, the glassy alloy havinga texture primarily composed of an amorphous phase and exhibiting atemperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x−T) _(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.
 18. An active filter comprising: aboosting converter circuit according to claim 16 ; and a control unitfor controlling the switching interval of the switching element of theboosting converter circuit.
 19. A filter comprising a capacitor and aninductor of a coil wound around a magnetic core, wherein the magneticcore comprises a molded article of a mixture of a glassy alloy powderand an insulating material, the glassy alloy having a texture primarilycomposed of an amorphous phase and exhibiting a temperature differenceΔT_(x), which is represented by the equation ΔT_(x)=T_(x)−T_(g), of atleast 20 K in a supercooled liquid, wherein T_(x) indicates thecrystallization temperature and T_(g) indicates the glass transitiontemperature.
 20. A filter according to claim 19 , wherein the rate ofchange in amplitude permeability of the magnetic core in a magneticfield of 2,000 A/m is within ±10% of an amplitude permeability in amagnetic field of 200 A/m, and the permeability of the magnetic core at100 kHz is in the range of 50 to
 200. 21. A filter according to claim 19, wherein the filter is a low-pass filter.
 22. A filter according toclaim 19 , wherein the glassy alloy is represented by the followingformula:(Fe_(1-a2)Ta₂)_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0<b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.
 23. An amplifying device comprising: an amplifier foroutputting a pulsed current and a filter connected to the output side ofthe amplifier for smoothing the pulsed current; wherein the filtercomprises a capacitor and an inductor of a coil wound around a magneticcore, wherein the magnetic core comprises a molded article of a mixtureof a glassy alloy powder and an insulating material, the glassy alloyhaving a texture primarily composed of an amorphous phase and exhibitinga temperature difference ΔT_(x), which is represented by the equationΔT_(x)=T_(x)−T_(g), of at least 20 K in a supercooled liquid, whereinT_(x) indicates the crystallization temperature and T_(g) indicates theglass transition temperature.
 24. An amplifying device according toclaim 23 , wherein the rate of change in amplitude permeability of themagnetic core in a magnetic field of 2,000 A/m is within ±10% of anamplitude permeability in a magnetic field of 200 A/m, and thepermeability of the magnetic core at 100 kHz is in the range of 50 to200.
 25. An amplifying device according to claim 23 , wherein the filteris a low-pass filter.
 26. An amplifying device according to claim 23 ,wherein the amplifier is a pulse-width-modulation amplifier.
 27. Anamplifying device according to claim 23 , wherein the glassy alloy isrepresented by the following formula:(Fe_(1-a2)Ta₂)_(100-x2-v2-z2-w2)Al_(x2)(P_(1-b2)Si_(b2))_(v2)C_(z2)B_(w2)wherein T represents at least one element of Co and Ni, and thesubscripts a2, b2, x2, v2, z2, and w2 satisfy the relationships,0≦a2≦0.15 by atomic ratio, 0≦b2≦0.8 by atomic ratio, 0 atomicpercent<x2≦20 atomic percent, 0 atomic percent<v2≦22 atomic percent, 0atomic percent<z2≦12 atomic percent, and 0 atomic percent<w2≦16 atomicpercent.